Archive for the ‘ethernet’ tag
Network Protocol Overhead
Here are some packet overhead numbers for a few popular protocols to help with doing bandwidth requirement calculations. This may be another add-as-we-go post, so please comment with additions or corrections.
Ethernet : 20 bytes
Frame Relay : 4 – 6 bytes
PPP : 6 bytes
MLPPP: 10 bytes
MPLS : 4 bytes
IP : 20 bytes
TCP : 20+ bytes
UDP : 8 bytes
GRE: 4 – 20+ bytesIPSec : 50 – 57 bytes
ESP : 20+ bytes
AH : 16+ bytes
L2TP : 24 bytes
RTP : 12 bytesBonus: A voice packet is always 40 bytes + data link since it will always (?) use RTP + UDP + IP.
Sources
CCNA Voice Official Exam Certification Guide (640-460 IIUC)
Encapsulating Security Payload
IIUC Notes – Getting Phones on the LAN
More study notes. Correct if wrong, though I hope I get some of it right since I already since I'm an R&S guy. :$
Switchport Configuration
- switchport mode access: This config makes the port an access port that carries the primary and voice VLAN traffic
- switchport mode trunk: This config akes the port a trunk unconditionally, but it will still send DTP messages
- switchport nonegotiate: This config keeps the port from sending DTP messages.
- switchport mode dynamic auto: If the port receives DTP messages, it will become a trunk. If not, it will be an access port.
- switchport mode dynamic desirable: The port actively sends DTP messages trying to become a trunk. This is the default configuration on a Cisco switch.
Cisco IP Phone Boot Process
- Phone connects to an Ethernet switch and gets power if needed
- Switch tells the phone the correct voice VLAN through CDP
- Phone sends DHCP request for its voice VLAN
- DHCP offer includes the TFTP server from which to download the config
- Phone downloads the config from the TFTP server
- Phone contacts the call processing server as dictated in the config file
DHCP Settings on a Cisco Router or L3 Switch
R1(config)#ip dhcp pool MYPOOL
R1(dhcp-config)#network 192.168.0.0 255.255.255.0
R1(dhcp-config)#default-router 192.168.0.1
R1(dhcp-config)#dns-server 192.168.0.10
R1(dhcp-config)#option 150 ip 192.168.0.20 <– Tells the phone to download the config from this TFTP server
R1(dhcp-config)#exit
R1(config)#ip dhcp excluded-address 192.168.0.1 192.168.0.100 <– Don't use these IPs when handing out DHCP
NTP
Why should you use NTP for a CME setup?
- Phones display correct time
- Voicemails have the correct time
- CDRs are timestamped accurately
- Router logs are timestamped accurately
- Time-based access worked predictably
R1(config)#ntp server 1.1.1.1
R1(config)#clock timezone MYTZ -5 <– Sets the timezone to a zone called MYTZ that's 5 hours behind UTC
IIUC Notes – Assigning Ephone-dns to Ephone Buttons
These are some of my notes on my IIUC studies. Since I am a novice as voice stuff, please let me know what I get wrong.
An ephone is a representation of a phone. It's basically a structure of features that a phone will have.
Configuration in CME:
R1(config)#ephone 34 <– This is just a tag and has nothing to do with an extension or phone
R1(config-ephone)#mac-address 1111.2222.3333 <– Assigns this ephone to the phone with that MAC address
An ephone-dn is a directory number that can be assigned to one or more phone. This is usually your extension and/or DID number.
Configuration in CME:
R1(config)#ephone-dn 18 <– Again, just a tag
R1(config-ephone-dn)#number 1000 <– the extension
Ephone-dns (i.e., extensions) are assigned to ephones through the button directive under the ephone setup. You can have more than one assignment per button command.
Configuration in CME:
R1(config)#ephone 34
R1(config-ephone)#button 1:18 <– Assigns extension 1000 (through ephone-dn 18) to button 1
The colon (:) in the button line is a separator that means that this is a normal ring phone – when someone dials that extension, your phone rings and lights up. There are other separator characters.
| Character | Function |
| : | Normal ring; the phone rings and lights up |
| b | Call waiting beep; the phone will light up, but there will be no ring. If you're on the line, you'll hear a beep on the line. |
| f | Feature ring; a triple ring |
| m | Monitor mode; lets you see the status of the line without being able to use it. Think of receptionists seeing if the boss is on the phone. |
| o | Overlay line without call waiting |
| c | Overlay line with call waiting |
| x | Overlay expansion with rollover |
| s | Silent; disable ringing and call waiting beep, but lights still flash |
| w | Watch mode; like monitor, except it monitors if any line on the phone being watched is active. If I have 4 ephone-dns on my phone and am on line 2, if you're watching line 1 of my phone, you'll see it as active |
Configuration in CME:
R1(config)#ephone 34
R1(config-ephone)#button 3m15 <– Monitors ephone-dn on button 3
R1(config-ephone)#button 4s82 <– Assigns ephone-dn 82 to button 4 but nothing will ring
R1(config-ephone)#button 5f31 <– Assigns ephone-dn 31 to button 5 with a triple ring
IIUC Notes – Powering Cisco Phones
Feel free to correct anything that is wrong or incomplete.
- Power over Ethernet (PoE)
- Can provide power to a Cisco phone, access point, security camera, etc., through the network cabling, eliminating the need to plug the phone into the wall for power.
- Generic term for providing power on the Ethernet cable
- Provides centralized power that can be put on a UPS
- Allows devices to be located away from power outlets
- Removes cabling clutter at the user's desk
- Can be provided through PoE-enabled switches, power panels or inline couplers (power injectors)
- Oversubscription is common
- If every device on a switch asks for full power, the switch may not be able to handle the load.
- Of course, devices can be powered with a power brick at the desk
- 802.3af
- IEEE standard for PoE from 2003
- Defines power classes so different devices can ask for different power levels
- Class 0: 15.4W allocated
- Used for el cheapo devices that just want power
- Class 1: 4.0W
- Class 2: 7.0W
- Class 3: 15.4W
- Class 0: 15.4W allocated
- Uses all 4 pairs of wire, so works on gig links
- Power procedure
- Small DC current is applied to the line
- If an 802.3af device is attached, it runs the current through a resistor
- The resistance is detected by the switch which can determine the class of power
- Power is applied to the device
- Cisco Inline Power
- Cisco's version of PoE created in 2000 (before 802.3af)
- Each device tells the switch what its power needs are
- Power procedure
- PoE device connected to the switch
- Switch sends Fast Link Pulse (FLP)
- If FLP is received back, 6.3W of power are applied
- Device boots off of 6.3W and tells the switch what its real power requirements are via CDP
Server NIC Aggregation to a Cisco Switch
Have you even noticed that your new servers all have 2 NICs on the board? At least all of them that I’ve seen in the last 3 years have. A lot of server admin actually use them in a NIC teaming scenario where both NICs are used as one logical device — much the same as Etherchannel on a switch. This provides some fault tolerance and availability in case of failure, which is good idea in most cases.
There are a few different ways to configure teaming on the box (usually called bonding in Linux), and each has its own advantages and disadvantages. The network dude(tte) may have to do some things on the switch side for some of them to work, though. If you’re want to run in link aggregation mode (mode 4), for example, the switch ports need to be in the same channel group to work appropriately.
Let’s look at mode 4 a little closer to see what we need to do. The scenario is that you have eth0 plugged into F0/15 of a 2950 and eth1 is in F0/16. You’ve seen the configuration for channelling between switches before, so you know the basics. Put the ports in the same channel-group and configure the proper Port-channel interface to do the work. In this case, we’re just configuring the ports to house a host instead of being trunks.
int F0/15 channel-group 1 int F0/16 channel-group 1 int Port-channel 1 speed 100 duplex full switchport switchport mode access
I detect at least one problem with our setup, though. Both NICs are plugged into the same switch; what happens when the switch goes down? The server goes away. Logic should tell you, then, to put the NICs in different switches to fix that, but you can’t do Ethernchannel on two different switches. The ports have to be in the same device for the aggregation to work. What’s the fix?
You can look at getting a nice chassis switch and putting each NIC in different modules. Modern IOS versions allow etherchanneling across modules, so, if one module fails, you still have that other. That would do it, but I’m sure you don’t have the money for a 4500 in the budget, right?
Another solution is to use a couple 3760s which, when connected using the StackWise cable, are one logical device. That gives you two separate switches that you can configure with the same channel group. An upgrade to this solution is to use a pair of 6500s with VSS 1440 modules in them so that you have a stack of 6500s! I’m sure that’s not expensive at all, though.
Send any white shoes questions my way.
Make Your Own Ethernet Cables
If you need to buy an Ethernet cable, you’ll pay quite a premium for it at your local CompUSA or Circuit City. $22.99 for a 7′ Ethernet cable is terrible. For just a few dollars more, you can buy a 250′ roll of cable and make 35 of them yourself. You’ll need to invest in a good crimper and some RJ45 heads as well, but that cost is quite small compared to how much you can save by making your own.
Your data center will look better if you make your own cables. If you buy a bunch of 10-footers and 50-footers and need to run 12 feet, what happens? You’re stuck running a 50-footer to the next rack. Do that a few times and you’ve got one of these. If you make your own, you can have custom lengths just the right length that look like this.
Being able to make your own Ethernet cables also lets you customize your cables. You can make straight-through cables for connecting to a switch, crossovers for creating uplinks, rollovers for making Cisco console cables, or null modem cables for connecting modems to serial ports. I haven’t made any other cables, but I’m sure there are dozens more types out there.
So, save money, clean up the data center, and make whatever you need. I won’t go into how to make them, but here’s a list of some places to show you how.
—-
- A pretty good video
- Some technical stuff on pinouts
- Some pretty detailed instructions on making a crossover
- A DIY kit from Amazon