Archive for the ‘ccnp’ Category
ROUTE Notes – More IGP Redistribution
As always, feel free to correct.
Study Notes
- When a router redistributes from one routing protocol to another, where does the router get the list of routes to redistribute?
From the routing table. Only IGP A’s routes (not topology or successors) are redistributed into IGP B’s domain.
- What are two methods of filtering redistributed routes?
Use a route-map in the redistribute line or a distribute-list.
- Of the two methods for filtering, which one has more options?
The route-map method has more options. You can match on all sorts of stuff, including an ACL or interface, and filter based on that.
- How does using distribute-lists differ between OSPF and EIGRP?
In EIGRP, distribute-lists are used to keep a route from being propagated. In OSPF, they’re used to keep routes from reaching the routing table. The effect is basically the same, but the cause is very different.
- How do I redistribute an EIGRP into OSPF as an E1?
You can set that that in the redistribute command. You can also match a route-map and set the metric-type there.
- What is a big pitfall of having two routes mutually redistribute the same two IGPs?
A router could redistribute IGP A’s routes into IGP B where the second router redistributes them back into IGP A. Potentially, either router could choose very long routes to get to a destination based on the different ADs and metrics of the IGPs.
- How can I keep this domain loop from happening?
Set the metrics of the redistributed routes so that the originating IGP has the preferred path
Set the AD on the redistributed routes so that the originating IGP has the preferred path
Manually filter routes so one IGP isn’t presented with its own routes
Use route-tags to mark redistributed routes to filter or manipulate later
- How do you change the metrics of the routes?
You can use the redistribute command to set the metrics. You can also use route-maps to match routes or tags and set the metric.
- How do I change the AD of the routes?
You can use the distance subcommand to set the AD on the whole domain or from a specific originating (or redistributing) router.
- How do I change the AD for route from 1.1.1.1 to 201?
R1(config-router)#distance 201 1.1.1.1 0.0.0.0
- How do I set a route-tag?
Use a route-map to match the routes you want to tag, and use the set tag directive.
- How does using EIGRP as one of my IGPs help me with mutual redistribution on multiple routers?
EIGRP actually has two ADs – 90 for internal and 170 for external routes. If a route is redistributed into EIGRP, it will have an AD of 170, so it will be less preferred than interal EIGRP, OSPF, or RIP routes. Unless you’re using internal BGP or custom ADs, this will keep a looping route out of the routing table and, thus, from being redistributed.
- How does using OSPF as one of my IGPs help me with mutual redistribution on multiple routers?
You may be able to use the metric-types to do some filtering, but the cool AD thing is for EIGRP only. Since external OSPF routes have an AD of 110 just like internal routes, you can’t rely on AD to keep the looping routes out like you can with EIGRP.
- How does using RIP as one of my IGPs help me with mutual redistribution on multiple routers?
RIP never helped anyone with anything. Just convert your RIP routers to EIGRP and be much happier.
- What’s a quick way to have OSPF set all external routes to an AD of 201?
R1(config-router)#distance ospf external 201
- What happens if I have OSPF redistributing into EIGRP redistributing into RIP (all mutually)?
You may wind up with a VERY long path without some intervention. You’ll need to do some filtering on the redistribution to keep routes short.
- Can’t I just use the redistribute command to set metrics coming in and out of all the IGPs to keep the looping routes out?
Yes, you can. If you have a small network, that shouldn’t be a problem. If you have a couple thousand routes, though, I’m sure people have better things to do than manage metrics.
- In what order do you configure the metrics when redistributing into EIGRP?
Bandwidth, delay, reliability, load, and MTU
- What’s weird about an extended ACL when using them with route filtering?
When matching routes, an extended ACL will use the ACL’s source field as the network of the route and the destination field as the subnet mask. For example, access-list 101 permit ip host 172.16.0.0 host 255.255.255.0 matches 172.16.0.0/24.
- What can’t route-maps do other clean the dishes?
They’re used in many, many places on a Cisco router. I imagine there’s a macro somewhere that will clean the dishes, though.
What Command Was That
What command…
- …shows the metric of the route you just redistributed into EIGRP?
show ip eigrp topology
- …shows the metric of the route you just redistributed into OSPF?
show ip ospf database external
- …shows the tag of a route?
show ip route
- …shows the admin distances you’ve messed up?
show ip protocols
- …shows the admin distance of a particular route?
show ip route x.x.x.x y.y.y.y
ROUTE Notes – IGP Redistribution
As always, feel free to correct.
Study Questions
- When you redistribute OSPF into EIGRP, what are you really redistributing?
Routes knows via OSPF
Networks of OSPF-enabled interfaces
- What’s the default cost of an EIGRP route redistributed into OSPF?
20
- What’s the default metric of an OSPF route redistributed into EIGRP?
There is none since EIGRP has all those nifty k-values that have to be processed. Routes actually won’t redistribute without them.
- How do you set the metrics of a route redistributed into EIGRP?
Set the default metric with the default-metric subcommand
Set the metric in the redistribute … metric subcommand
Set the metric with a route-map in the redistribute … route-map subcommand
- If you have a default metric set under EIGRP and a metric set on a redistribution of OSPF, which does the router use?
The router uses the metric for the redistribution.
- What’s special about the metric when redistributing one EIGRP AS into another?
The metric is copied from one AS to the other.
- What is I redistribute one OSPF domain into another?
The same thing happens – the metric is copied from the originating domain.
- What’s the difference in AD between an EIGRP and an external EIGRP route?
EIGRP: 90
External EIGRP: 170 [Didn't I do a blog post about this last month?]
- What’s the difference between an external type 1 and an external type 2 OSPF route?
External 2 routes, only the external cost is used; no router increments the cost. For external 1 routes, the external cost is incremented by each route with the internal cost.
- Which of O E1 and O E2 routes is more preferred and why?
E1s are preferred because they’re considered more accurate. [Didn't I blog on this last month, too?]
- I have redistribute eigrp 1 configured in my OSPF config, but 10.0.0.0/24 isn’t showing up in OSPF. What gives?
OSPF only redistributes classful routes unless you add the subnets option to the redistribution command.
- What are the options in the redistribute directive when redistributing OSPF into EIGRP?
redistribute ospf process-id [ metric bandwidth delay reliabilityload mtu ] [ match { internal | nssa-external | external 1 | external 2 } ] [ tag tag-value ] [ route-map route-map ]
- What are the options in the redistribute directive when redistributing EIGRP into OSPF?
redistribute ospf process-id [ metric metric ] [ metric-type metric-type ] [ match { internal |nssa-external | external 1 | external 2 } ] [ tag tag-value ] [ route-map route-map ] [ subnets ]
- What do type-4 LSAs do?
If an external route comes from another area, the ABR uses type-4 LSAs to advertise the cost of the route from the ABR to the ASBR. Routes use this cost as a tie breaker if the internal cost is the same from two ABRs.
- What type of LSA are used to flood routing advertisements from an external NSSA area into area 0?
The NSSA ASBR uses type-7s to flood into the NSSA, but the ABR to area 0 converts those to type-5s.
What Command Was That
What command…
- …show all the EIGRP routes that originated from other routing protocols?
show ip route eigrp | inc ^D EX
- …shows all the OSPF routes that originated from other routing protocols?
show ip route ospf | incl ^O E[12]
- …show all the type-4 LSAs floating around in an OSPF area?
show ip ospf database asbr-summary
- …show the cost to get from a router to an ASBR?
show ip ospf border-routers
ROUTE Notes – OSPF Virtual Links and Frame Relay Stuff
Feel free to correct. I feel like I’m missing a big piece here, so please fill in a gap if you see one. Thanks. :)
Study Questions
- How many area 0s (zero) can you have in an OSPF implementation
Just one.
- If my company merges with another company, and we’re both running OSPF, how can we get our networks routing together properly?
The easiest thing to do is to connect your two area 0s together through some physical link. If you can, you can use virtual links to connect an ABR to another ABR to extend the zones together.
- How do you configure virtual links?
R1(config-router)#area 1 virtual-link 1.1.1.1
- That IP in the virtual link command looks like a loopback. What’s up with that?
It’s the RID of the router to which you want to connect.
- Why wouldn’t I just use a GRE tunnel between my two routes and put that in zone 0?
That’s a good question. I would probably do that instead of virtual links if I had the choice because it eliminates any weird problems you may see with the virtual links. [Someone pipe up on this one, please.]
- What types of authentication can you do with virtual links?
None
Clear text
MD5
- I’ve configured frame-relay map ip 1.2.3.4 101 on my s0/0/0.1, but I can’t get a neighbor to come up. What gives?
A non-broadcast medium can’t detect neighbors dynamically. You need static neighbors, or you can add the broadcast keyword to the end of your map statement.
- What is the big problem with partial mesh frame relay topologies when OSPF comes into play?
Not all routers are connected directly, so some routes won’t see all the neighbors. When OSPF routes propagate on broadcast medium, the next-hop is the router what propagated it; you’ll wind up seeing routes to routers to which you don’t connect.
- How do you get over the partial mesh problem?
You can statically configure frame relay maps pointing the IPs of the unconnected routers to the DLCI of a router that is connected to them (like a central hub router).
- What network types use DRs and BDRs?
Anything multiaccess, so the NBMA and BMA.
- Which network types can dynamically discover neighbors?
Broadcast and point-to-multipoint
- Why do you have to configure static neighbors on NBMA and point-to-multipoint non-broadcast links?
Since OSPF uses multicast to talk to neighbors, a router treats the packets like a broadcast. Since these network types don’t have a broadcast capability, the only way a neighbor will be established would be through static statements.
- You have a hub-and-spoke topology over a frame relay cloud. One of your hubs sees routes for all the networks at the other other hub sites. Is all as well as it seems?
No. The routes to the other hub networks will have their next hop set to the frame relay IP of each hub router. Since one hub router can’t get directly to others, the router won’t be able to pass traffic to those sites at all. You’ll need to statically map those IPs to the DLCI of the hub site for traffic to flow as expected.
What Command Was That
Which command(s)…
- …define a virtual link using the MD5 has of the key “test”?
R1(config-router)#area 1 virtual-link 1.1.1.1 authentication message-digest
R1(config-router)#area 1 virtual-link 1.1.1.1 message-digest-key 1 md5 test
- …configure a static OSPF neighbor?
R1(config-router)#neighbor 1.2.3.4 [cost X] [priority Y]
- …shows the status of a virtual link?
show ip ospf virtual-links
show ip ospf neighbor
- …shows the authentication type and youngest key for a virtual link?
show ip ospf virtual-links
- …displays the network type for an interface?
show ip ospf interface
ROUTE Notes – OSPF Filtering and Summarization
Feel free to correct all this stuff. Additions are also welcome.
Study Questions
- How do I keep an area route from reaching a router in that area?
You don’t. That defeats the whole purpose of having the topology database on every router. If you filtered one route from a router, there’s no way that SPF could calculate routes correctly.
- Fine, then. Where do I filter routes?
You filter routes on an ABR or ASBR. Since routers only have the whole topology for their area, it’s safe to filter routes from another area or from a redistributed routing protocol. On a more technical note, you’re filtering type-3 LSAs on an ABR and type-5 LSAs on an ASBR.
- Show me an example of keeping the area 1’s route of 192.168.0.0/24 from hitting area 0.
R1(config)#ip prefix-list PL1 deny 192.168.0.0/24
R1(config)#ip prefix-list PL1 permit 0.0.0.0/0 le 32
R1(config)#router ospf 1
R1(config-router)#area 0 filter-list prefix PL1 in
- How about keeping a router from even learning about that same route from area 1?
R1(config)#router ospf 1
R1(config-router)#area 1 filter-list prefix PL1 out
- You know that that seems a little backwards, don’t you?
You have to think of filtering in terms of the area instead of in terms of the router. You’re filtering into the area or out of the area…not into or out of the router.
- How do you keep the OSPF route to 192.168.0.0/24 from being submitted to the routing table?
I’ll use the same prefix list above.
R1(config)#router ospf 1
R1(config-router)#distribute-list prefix PL1 in
- Isn’t that almost the same syntax to filter EIGRP routes?
Almost.
- How do I send area 1 the summary route of 192.168.0.0/16 from area 0? That would be a type-3 LSA.
On the ABR: R1(config-router)#area 1 range 192.168.0.0 255.255.0.0
How do I do the same thing for external routes (type-5 LSAs)?
On the ASBR: R1(config-router)#summary-address 192.168.0.0 255.255.0.0
- If you see “totally” in the stub area description, what does that mean?
Someone at Cisco is a surfer. It also means that there are no type-3 LSAs in that area.
- Is the term “stubby” an insult?
No. It’s a term for an OSPF area that has certain types of LSAs filtered. Summary routes are usually involved. This is not filtering that we discussed above, though. This is keeping all instances of an LSA type from entering an area.
- What the heck is a type-7 LSA?
If an NSSA has an external route it needs to flood, it uses a type-7 instead of a type-5. This allows a router in a NSSA to advertise external routes without being bombarded by type-5s from other areas.
- What are the four types of stubby areas? What LSA types do they filter? What LSA types do they allow?
Stub – filters type-5s – allows type-3s
Totally stubby – filters type-3s and type-5s
NSSA – Filters type-5s – allows type-3s and type-7s
Totally NSSA – Filters type-3s and type-5s – allows type-7s
- What area can never be a stubby?
Area 0, of course.
- If area 1 is a stub, what LSA types will area 0 see from it?
Type-3s. The routes from area 1 are still advertised into area 0 as normal.
- How about if area 1 is a totally NSSA?
Type-3s and type-5s. The routes from area 1 are still advertised into area 0 as normal, and the type-7s would be translated to type-5s. [Someone check me on this one.]
- Where do you configure an area to be a stub?
On all the routers in the area. The same goes for NSSA.
- Where do you configure an area to be a totally stubby?
The totally stubby part is configured on the ABR. The other routers in the area should be configured as stub. The same goes for totally NSSA.
- What route always shows up in a stubby or totally stubby area unless someone has done something weird?
0.0.0.0/0
- Speaking of the default route, how do you manually summarize the default route in OSPF?
You can use the area 1 range 0.0.0.0 0.0.0.0. You can also use the default-information originate command in OSPF.
- What would you see on the internal routers if you had an ABSR that only had full BGP tables from your ISP configured with default-information originate?
You would see nothing. You need to have a default route somewhere for the router to advertise into OSPF. Since BGP full routes don’t contain a default, it won’t advertise.
What Command Was That
What command…
- …shows what type of stubby area an area is configured to be?
show ip ospf
ROUTE Notes – OSPF Neighbor Relationships
Feel free to correct.
Study Questions
- What are the definitions of the hello and dead intervals?
The hello intervals is how often a router sends hello messages. The dead interval is how long to wait before considering a neighbor dead from lack of hello messages; this is 4x the hello interval by default.
- How do you keep OSPF from trying to detect neighbors on an interface?
Don’t configure a network statement for that interface
Make that interface passive
- What type of routers connect to multiple areas?
Area border router (ABR)
- What fields in the hello packet need to match in order for a router to neighbor with another via OSPF?
Subnet
Area
Hello and dead intervals
IP MTU
Authentication method
Authentication key
- What’s another way to put an interface into an OSPF area other than the old network statement?
R1(config-if)#ip ospf 1 area 0
- Don’t the process IDs have to match?
No.
- How is the router ID calculated?
The router ID is discovered just as EIGRP does it. First, it looks for a route-id command. If one does not exist, the highest IP of on a up/up loopback interface is used. If one does not exist, the highest IP of the rest of the up/up interfaces is used.
- What is the protocol, source, and destination in an OSPF hello packet?
OSPF used protocol 89 (not TCP or UDP) sourced from the interface sending the packet to 224.0.0.5.
- What happens after neighbors are brought up successfully?
Topology databases are exchanged. Each router sends all the information it has about the area to its new neighbor.
- What would happen if the MTUs of two potential neighbors was different?
The routers will become neighbors, but the topology exchange will not occur successfully. [I think I’m missing a piece here. This seems very prescriptive in a situation where I would expect more chaos.]
- What types of authentication can be configured with OSPF?
None (type 0)
Cleartext (type 1)
MD5 hash (type 2)
- How do you configure a router to use MD5 authentication with OSPF?
R1(config-router)#area 0 authentication message-digest
- That didn’t work. What are we missing?
You have to set the key, dummy. Do that on the interface.
R1(config-if)#ip ospf message-digest-key 1 md5 KEY
- What is a DR? How about a BDR?
A designated router (DR) is a router that has been elected to advertise all the router for a multi-access segment (like a LAN segment). Every time a change occurs in the network, the router that detected it will notify the DR, who will then relay the information to the other routers on that segment. The backup designated router (BDR) takes over that functionality if the DR fails.
- What are the default hello intervals for broadcast, point-to-point, NBMA, and point-to-multipoint interfaces?
Broadcast: 10 sec
P-P: 10 sec
NBMA: 30
P-M: 30
- How do you change the default hello timer?
R1(config-if)#ip ospf hello-interval X
- What types of segments use DRs and BDRs?
Only broadcast and NBMA segments use DRs and BDRs.
- What are some important states of an OSPF neighbor? [Yes, there are others.]
INIT: A router has received a hello from another router, but its own hello has not been acknowledged.
2WAY: A router has received a hello and a acknowledgement from another router
EXSTART: The DRs and BDRs are elected, and exchanges are beginning with them
FULL: The router has successfully exchanged topology data with the neighbor
What Command Was That?
What command…
- …shows all the OSPF neighbors?
show ip ospf neighbor
- …shows the number of OSPF neighbors on an interface?
show ip ospf interface
- OR -
show ip ospf interface brief
- …shows the DR and BDR on an interface?
show ip ospf interface
- …shows the authentication method used?
show ip ospf interface
- …shows the hello and dead intervals configured on the router?
show ip ospf interface
- …shows the OSPF network type for an interface?
show ip ospf interface
- …shows the state of a neighbor?
show ip ospf neighbor
- OR -
show ip ospf neighbor detail
ROUTE Notes – Controlling Routes in EIGRP
Corrections welcome.
Study Questions
- Why would you ever want to summarize routes?
Summarizing routes minimizes the routes advertised to the network. For example, instead of advertising 192.168.0.0/24, 192.168.1.0/24…192.168.n.0/24, a router can advertise a single route to 192.168.0.0/16. Keeping routing tables small saves hardware resources, minimizes convergence times, helps avoid route flapping, and makes the routing table easier to read for humans.
- When will an EIGRP router auto-summarize a route?
If a router has interfaces that that are in different classes of network (Class A, B, C), then that router will auto-summarize those routes up to the classful boundary. For example, if you have a 10.0.0.1/24 and a 192.168.100.1/30, the router will advertise 10.0.0.0/8 and 192.168.100.0/24.
- You have two routers advertising the same summarized route. How do you make one preferred over the other?
Adjust the delay or bandwidth so one is favored.
- What is suboptimal forwarding in regards to summarization?
A summary route could be advertised from a router that’s not in the optimal path to the destination. If that route is chosen by a downstream router, traffic is passed to that router instead of a more optimal path through another router.
- How do you avoid suboptimal forwarding in regards to summarization?
Disable summarization. Advertising real networks will result in the optimal path being calculated.
- How do you manually summarize the route 192.168.100.0/22?
R1(config-if)#ip summary-address eigrp 1 192.168.100.0 255.255.252.0
- When will a summarized route stop being advertised by a router?
When the router no longer has any routes that fall inside the summary route, the summary is removed. That is, if a router is advertising 192.168.100.0/22, the route will be removed if the router no longer has ANY routes that are in the 192.168.10[0123].0 networks.
- What’s the biggest route a router can summarize?
The default route.
- What are two ways to advertise a default route in EIGRP?
Advertise a static default route through redistribute static
Summarize 0/0 out of an interface
- How do you keep one part of the network from having a route to another part of the network?
This is done with route filtering.
- When configuring route filtering in EIGRP, what’s the big keyword?
distribute-list
- What are the three techniques for filtering routes?
ACLs
Prefix lists
Route-maps
- Do you mean to tell me that route filtering also uses ACLs and route-maps?
Yes. Welcome to Cisco Systems.
- How do you use an ACL to filter out the route 192.168.0.0/24?
access-list 1 deny 192.168.0.0 0.0.0.255 access-list 1 permit any router eigrp 1 distribute-list 1 out
- How do you use a prefix list to filter out the route 192.168.0.0/24?
ip prefix-list PL1 deny 192.168.0.0/24 ip preffix-list PL1 permit 0.0.0.0/0 le 32 router eigrp 1 distribute-list prefix PL1 out
- How do you use a route-map to filter out the route 192.168.0.0/24?
access-list 1 permit 192.168.0.0 0.0.0.255 route-map RM1 deny 10 match ip address 1 route-map RM1 permit 999 router eigrp 1 distribute-list route-map RM1 out
-OR-
ip prefix-list PL1 permit 192.168.0.0/24 route-map RM1 deny 10 match ip address prefix-list PL1 route-map RM1 permit 999 router eigrp 1 distribute-list route-map RM1 out
What Command Was That?
What command…
- …shows you the prefix lists configured?
show ip prefix-list
- …shows the summary route being advertised for a particular network?
show ip route 192.168.0.0 255.255.0.0 longer-prefixes
- …shows what networks are being summarizes on a router?
show ip protocols
- …shows what route a router considers to be a default candidate?
show ip route (look for the *)
- …shows the default network?
show ip route
ROUTE Notes – EIGRP Topology Stuff
Study Questions
- How do you keep EIGRP from killing your WAN?
You can use the ip bandwidth-percent eigrp AS X command to limit the amount of bandwidth that EIGRP uses to update neighbors.
- How does EIGRP calculate how much bandwidth it can use for each frame relay PVC?
By default, EIGRP takes 50% of the (sub)interface’s configured bandwidth (with the bandwidth command) to use for updates on NBMA (non-broadcast mutliaccess) networks like frame relay. This value is divided equally among all the PVC configured on that interface.
- Why should you use delay instead of bandwidth to manipulate EIGRP?
There are other mechanisms, like QoS, that use bandwidth, so changing that value would affect those mechanisms. Only EIGRP uses delay.
- What’s the difference between the feasible distance (FD) and the reported (advertised) distance (RD)?
Feasible distance is the EIGRP metric value after the router has added it’s own information like bandwidth and delay to the formula. The reported distance is what a router calculates before it has added it’s own values. Essentially, the FD of one router is the RD of the next.
- What is an offset list?
An offset list is a way to artificially increment the FD and RD of a route or set of routes.
- You can add the load k-value into the metric calculation in EIGRP, but it’s not generally a good idea. Why?
The load is constantly changing as traffic changes on an interface. This would cause a constant stream of updates as traffic flows change.
- How often does a router send its full EIGRP topology table?
When new neighbors come up, the neighbors exchange their full tables, but, from that point forward, only updates are sent.
- When we talk about bandwidth in EIGRP, what are we actually talking about?
The bandwidth is actually the bandwidth of the slowest link between a router and the destination network. This is what’s used in the calculations.
- Assuming we’re using k1 and k3, what is the formula for calculating the metric?
metric = 256 * ( 10^7 / bandwidth [in kbps] + cumulative delay )
- You’ve decided to use k2 in your metric calculations, so you add that to a router. What happens to all the neighbors?
The neighbors all drop and start generating a “K-value mismatch” error.
- What is a successor? Feasible successor?
A successor is the EIGRP route for a particular network entry with the lowest metric. This is the route that EIGRP submits to the routing table for inclusion. A feasible successor (FS) is another EIGRP whose RD is lower than the successor’s FD; feasible successors can be used as an alternate path to a network if the successor goes away somehow.
- Where would you run into split horizon issues with EIGRP?
Split horizon says that you don’t advertise a route over the interface on which it was received. If you have a multipoint WAN link of some kind, routes from one spoke won’t be passed to another spoke through the hub.
- In what unit is the delay directive?
Tens of microseconds (10 * usec). That means that delay 1000 is 10,000 usec, or 10 ms.
- How does EIGRP do unequal cost path load balancing?
You can set the maximum-paths value under EIGRP to set the maximum number of equal paths that can be used. You also set the variance command there with a multiplier integer. The variance is multiplied by the successor’s FD, and any feasible successor whose metric is less than this new number is considered equal cost.
- What is an EIGRP stub router?
A stub router only receives routes via EIGRP and does not send them to other EIGRP neighbors. Since all the other routers know a router is a stub, they won’t send query messages to the stub router if they’re looking for a route. This will cut down on time waiting in active state.
- What is “stuck in active”?
If a successor for a network becomes unavailable and there are no FSes, a router will query each of its neighbors for a new routes to that network. If that router does not have a route, it will then ask its own neighbors, etc. In the meantime, the original router is still waiting for everyone to answer (that is, the route is in the active state) and will wait patiently until that happens. This could take a long time and result in a several-second outage to the queried network.
- By default, which types of routes are sent to EIGRP neighbors from a stub router?
Connected and summary
What Command Was That?
What command…
- …disables split horizon on an interface?
R1(config-if)#no ip split-horizon eigrp 1
- …sets the delay of an interface to 10ms?
R1(config-if)#delay 1000 (remember the tens of usec unit)
- …restricts the amount of bandwidth that EIGRP uses to 20% of the total bandwidth on an interface?
R1(config-if)#ip bandwidth-percent eigrp 1 20
- …apply an offset list to interface F0/0?
R1(config-router)#offset-list ACL in OFFSET F0/0
- …show the metrics of all the EIGRP routes a router has recieved for a network?
show ip eigrp topology 192.168.0.0/24
- …shows the successors and feasible successors for a network?
show ip eigrp topology 192.168.0.0/24
- …shows if a neighbor is a stub?
show ip eigrp neighbor detail
- …shows the maximum-paths and variance values?
show ip protocols
ROUTE – Redistribution Nuance #2 – OSPF External Metric Types
Last time, we talked about a nifty little lab I set up for redistribution and how the OSPF ASBRs acted a little differently than I expected. This time, let’s look at how changing external OSPF routes to a metric-type of 1 (E1) affects the routing tables.
Here’s the network again.
The static routes are being redistributed into their respective IGPs, and EIGRP is being redistributed into OSPF. Let’s look at the routing table on R1.
Gateway of last resort is not set
10.0.0.0/8 is variably subnetted, 7 subnets, 2 masks
O 10.0.0.2/32 [110/11] via 192.168.0.102, 00:06:53, Ethernet0/0
O E2 10.0.0.3/32 [110/20] via 192.168.0.105, 00:06:53, Ethernet0/0
[110/20] via 192.168.0.102, 00:06:53, Ethernet0/0
S 10.10.10.0/24 is directly connected, Null0
C 10.0.0.1/32 is directly connected, Loopback0
O E2 10.0.0.4/32 [110/20] via 192.168.0.105, 00:06:53, Ethernet0/0
[110/20] via 192.168.0.102, 00:06:53, Ethernet0/0
O 10.0.0.5/32 [110/11] via 192.168.0.105, 00:06:53, Ethernet0/0
O E2 10.10.20.0/24 [110/20] via 192.168.0.105, 00:06:03, Ethernet0/0
C 192.168.0.0/24 is directly connected, Ethernet0/0
O E2 192.168.101.0/24 [110/20] via 192.168.0.105, 00:06:53, Ethernet0/0
[110/20] via 192.168.0.102, 00:06:53, Ethernet0/0
Notice that there are two routes to each of the networks discovered from EIGRP (the loopbacks of 10.0.0.3/32 and 10.0.0.4/32 as well as 192.168.101.0/24). There is nothing strange here; OSPF simply sees the exit paths through the ASBRs. How about if we change the metric-type on the routes from R2 and see what happens?
I know of at least two ways you can do it. First, you can set the metric-type in the redistribute command on the ASBR’s OSPF process.
redistribute eigrp 1 subnets metric-type 1
You can also use a route-map to set the metric-type and apply that to the redistribute command.
route-map TEST permit 10 set metric-type type-1 ! redistribute eigrp 1 route-map TEST subnets
Either way does the same thing. Now let’s check the route table on R1 again.
Gateway of last resort is not set 10.0.0.0/8 is variably subnetted, 7 subnets, 2 masks O 10.0.0.2/32 [110/11] via 192.168.0.102, 00:18:30, Ethernet0/0 O E1 10.0.0.3/32 [110/30] via 192.168.0.102, 00:02:11, Ethernet0/0 S 10.10.10.0/24 is directly connected, Null0 C 10.0.0.1/32 is directly connected, Loopback0 O E1 10.0.0.4/32 [110/30] via 192.168.0.102, 00:02:11, Ethernet0/0 O 10.0.0.5/32 [110/11] via 192.168.0.105, 00:18:30, Ethernet0/0 O E2 10.10.20.0/24 [110/20] via 192.168.0.105, 00:17:40, Ethernet0/0 C 192.168.0.0/24 is directly connected, Ethernet0/0 O E1 192.168.101.0/24 [110/30] via 192.168.0.102, 00:02:11, Ethernet0/0
Only one route this time, and it’s the E1 route from R2. It seems that E1 routes are more preferred than E2 routes. Let’s look at the OSPF database for 192.168.101.0/24 on R1 to see if we can figure that out.
R1#sh ip ospf database external 192.168.101.0 OSPF Router with ID (10.0.0.1) (Process ID 1) Type-5 AS External Link States Routing Bit Set on this LSA LS age: 467 Options: (No TOS-capability, DC) LS Type: AS External Link Link State ID: 192.168.101.0 (External Network Number ) Advertising Router: 10.0.0.2 LS Seq Number: 80000004 Checksum: 0xEA58 Length: 36 Network Mask: /24 Metric Type: 1 (Comparable directly to link state metric) TOS: 0 Metric: 20 Forward Address: 0.0.0.0 External Route Tag: 0 Routing Bit Set on this LSA LS age: 1497 Options: (No TOS-capability, DC) LS Type: AS External Link Link State ID: 192.168.101.0 (External Network Number ) Advertising Router: 10.0.0.5 LS Seq Number: 80000001 Checksum: 0x6260 Length: 36 Network Mask: /24 Metric Type: 2 (Larger than any link state path) TOS: 0 Metric: 20 Forward Address: 0.0.0.0 External Route Tag: 0
You can see that everything is the same except for the metric-type field, which is exactly what we expect. By definition, if an external OSPF route is E1, the internal OSPF cost is added to the total cost of the route. This is reflected in the “Comparable directly to link state metric” text next to the Metric Type value. In contrast, an E2 route does not have the cost incremented; the cost is simply passed down the line as “Larger than any link state path”. This means that E1 routes are considered more accurate and should be more preferred than E2 routes.
Just another complexity of OSPF. Thanks to @matthewnorwood, @jameskazin, @steve, @wannabeccie, @ciscotophat, and @lbsources for the insight into the route differences.
Send any twitter updates questions my way.
Audio Commentary
Audio clip: Adobe Flash Player (version 9 or above) is required to play this audio clip. Download the latest version here. You also need to have JavaScript enabled in your browser.
Stubby Post – VTP Clients Send Updates
VTP clients send VLAN updates. Did you know that?
I had a VTP server and client in the same VTP domain, and, when I cabled up the trunk, the client overwrote the VLAN database on the server.
The moral of the story is that the best revision number will win no matter what the operating mode of the switch.
SWITCH – Epic Fail
I did my standard 2ish-hour drive to the closest testing center today to take the SWTCH test (642-813). Utter failure. That’s 3 for those scoring at home.
The test was the absolute worst I’ve ever taken. I know that I complain a lot, but this is totally justified in my eyes. My 4th grade spelling tests were better than this. I’ve seen kindergarten plays with better production value.
First of all, it was poorly written. Whoever wrote those questions has a few pieces of information about English sentence structure missing from their skill set. A sentence needs a verb, right? Well, a lot of the sentences were missing those. It’s kind of important to know what the whole point of the sentence is, or is that too much to ask? The “drag this over here” exercise questions all started with the same 13-word phrase that left the question so long that it was unreadable. A couple of commas would have been nice in some. Others I just had to infer from the answers what they were trying to ask.
There were lots of spelling errors as well. Most of them were just stupid stuff like switched letters or missing characters, but, at one point, I had to figure out that I needed to look at the “router” instead of the “route”. That’s not really cool. The misspellings were so bad that they were actually misspelling the hostnames on the diagrams provided. Does anyone even try any more?
Let’s talk about the technical level of the test. If I didn’t know any better, I would swear I was taking a CCNA test. The technical material was so elementary that it bordered on comical. If I recall correctly (which I never do), there were about 3 questions on trunking which were so easy that my wife could answer them. There were about 4 FHRP questions that were out of the “Cisco for Dummies” book. I could go on, but I have better things about which to complain.
“So,” you might ask, “why did you fail it if it was so easy?” That’s a great question. I failed it because the name of the test is misleading. When Cisco says “Implementing Cisco IP Switched Networks”, they really mean “Collecting Documentation About VLANs.” There were at least four questions on this test that asked what information you need to collect before implementing some unknown step of a project involving VLANs. Sometimes, the reference was to rollback plans. Sometimes it discussed IP assignments. Sometimes it even talked about collecting user requirements. It seemed that nearly half of the questions on the test discussed planning for making changes or preparing change documentation. There was very little “implementing.”
To top it all off, too, one of my labs froze. I entered a command into a router, and it didn’t come back. I couldn’t change to the other lab windows, either (the “Scenario” or “Topology” windows included), but my timer kept ticking. I could click around in the testing software, but the lab itself was toast. I got the administrator who helped me out a bit after the machine was rebooted. I didn’t run out of time or anything, but getting up to find help to troubleshoot a problem really throws you off.
How about some closing words? First of all, I have given up on the Cisco Press books and other materials. Each time I use them they have little to no coverage about topics on the test itself. The ISCW was that way, and we all know about my problems with the ONT. I figured that those were just aged text, but SWITCH is only a month or two old, isn’t it? That means the test hasn’t had that much time to change, but the materials are totally different already.
I actually have an example of the books leading the reader directly away from the test materials. I’m reading from the “CCNP SWITCH 642-813 Quick Reference” book by Donohue. On page 8, it discusses the PPDIOO lifecycle approach.
Network engineers at the CCNP level will likely be involved at the implementation and following phases. They can also participate in the design phase.
That doesn’t make any sense, does it? Didn’t I just say that there were a good number of questions on preparation (the first P) and planning (the second P). Both of those come before the design phase.
Somebody help me out here. What am I missing? Is there some magical book series that has the answers?
I should have bought testing vouchers in bulk when they were $150.
Audio commentary
Audio clip: Adobe Flash Player (version 9 or above) is required to play this audio clip. Download the latest version here. You also need to have JavaScript enabled in your browser.
UPDATE: It seems that the idea of seeing topics on the exam that aren’t are the test go beyond just me. I’m getting in touch with as many people related to the SWITCH book as I can to let them know that this is a serious problem. I’m sure I’ll have a post or two on the outcome of that effort.