Tuesday, January 29, 2013

GE/10GE in the Core

Hi everyone, this post is about ethernet in the core. Yes, it still covering GE/10GE standards and doesn't include 40/100GE. I expect, that it will be covered in CCIE SP version 4. And hopefully, i will try to pass the written v4 for recertification :))

The ethernet topic is usually well known and nobody expects "hard" questions. Anyway I prefer to refresh my memory by using Cisco docs. Maybe I'm missing some Cisco marketing terms (like VTXP in IPoDWDM post), etc. :))

This post includes following topics:
  1. Gigabit Ethernet standards
  2. 10 Gigabit Ethernet standards
  3. Duplex Mode
  4. MTU
  5. Flow control
  6. Link Aggregation Control Protocol
  7. 802.1Q VLAN sub-interface


The MTU = MTU - 4 bytes FCS, i.e. default MTU value is set to 1514 for normal interface and 1518 for dot1q enabled interface.

Flow Control

The flow control used on 10-Gigabit Ethernet interfaces consists of periodically sending flow control pause frames. It is fundamentally different from the usual full- and half-duplex flow control used on standard management interfaces. Flow control can be activated or deactivated for ingress traffic only. It is automatically implemented for egress traffic.


LACP is interesting topic. By the standard there is only single interval for LACP hellos - 1 second. Cisco in the documentation states, that they support "fast" lacp timers, i.e. less than a second and, of cause,  this is standard incompatible proprietary extension. How many hours spend on implementing all this "fast" helloes for each and every protocol - hopefully, we have a solution today - BFD. Of cause, the BFD over LAG is still under discussion - some vendors implemented it as a single BFD session over LAG, others implemented in smarter way - BFD session over each LAG constituent port.

IOS Config Example:
Router> enable
Router# configure terminal
Router(config)# lacp system-priority 23456
Router(config)# interface g4/0/0
Router(config-if)# lacp port-priority 500
Router(config-if)# end

802.1Q VLAN Sub-interface

This is simple part.

IOS Example:
interface FastEthernet0/0.100
 encapsulation dot1Q 100
 ip address
 IOS XR Example:
RP/0/RP0/CPU0:router# configureRP/0/RP0/CPU0:router(config)# interface TenGigE 0/2/0/4.1 RP/0/RP0/CPU0:router(config-subif)# dot1q vlan 10RP/0/RP0/CPU0:router(config-subif)# ipv4 address interface TenGigE0/2/0/4.2 RP/0/RP0/CPU0:router(config-subif)# dot1q vlan 20RP/0/RP0/CPU0:router(config-subif)# ipv4 address RP/0/RP0/CPU0:router(config-subif)# interface TenGigE0/2/0/4.3 RP/0/RP0/CPU0:router(config-subif)# dot1q vlan 30RP/0/RP0/CPU0:router(config-subif)# ipv4 address RP/0/RP0/CPU0:router(config-subif)# commitRP/0/RP0/CPU0:router(config-subif)# exitRP/0/RP0/CPU0:router(config)# exit

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