This chapter has touched on the two different MC-LAG modes:
active-active. When MC-LAG was first released,
the only available mode was
active-standby, which works on both DPC and MPC
line cards. Because it was the first mode to be released and because of
the simplicity of its design, the
active-standby mode is generally more common.
With the introduction of Trio and MPC line cards, MC-LAG was upgraded to
active-active mode. This new
mode will only work using Trio-based line cards such as the MPC.
active-standby mode works
by selecting a PE router to be the active node while the other PE router
is the standby node. Only one of the PE routers can be active at any
given time. When a PE router is active, it will signal via LACP to the
CE router its child link is available for forwarding.
Figure 8-9. MC-LAG Mode Active-Standby.
Figure 8-9 illustrates MC-LAG
active-standby mode. In this
PE1 is active and
PE2 is the standby node. This mode
forces all traffic through the active node
PE1. For example, a frame destined to VLAN 100
would be forwarded to
PE1 and then
H1. A frame destined to
VLAN 200 would also be forwarded to
PE1, then to
PE2, and finally to
Let’s take a look at the LACP information from the vantage point
show lacp interfacesAggregated interface: ae1 ...