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Is IS-IS Applicable to the Network Where One CE Is Dual-Homed to Two PEs?

Latest reply: Dec 24, 2018 01:25:44 923 2 0 0 0

Hello everyone,

Today, I'd like to show you whether IS-IS is applicable to a network where a CE is dual-homed to PEs.

Is IS-IS Applicable to the Network Where One CE Is Dual-Homed to Two PEs?
IS-IS can be used in the network where one CE is dual-homed to two PEs. In IS-IS andOSPF, the configurations of the networking where one CE is dual-homed to two PEs are different.
Figure1 and Figure 2 show two applications of CE-PE dual-homing.
Figure 1 Networkingdiagram of CE-PE dual-homing 1

Figure 2 Networkingdiagram of CE-PE dual-homing 2

As shown in the networking, a PE imports BGP routes to IS-IS and thus IS-IS on thePE can advertise the routes to the peer PE through a CE. IS-IS on the peer PElearns the routes as IS-IS routes. By default, IS-IS routes are prior to BGProutes. Thus, the RM module prefers the IS-IS routes and then BGP routes becomeinactive. In this case, the PE cannot import the BGP routes, causing routeflapping.

IS-IS is not as good as OSPF in preventing route loops. OSPF marks imported BGProutes with DN bits to prevent route loops. IS-IS does not provide mechanismsto prevent route loops. Thus, IS-IS needs to tag the BGP routes it imports.After learning the routes, the peer PE filters out the routes through policies. 

This is what I want to share with you today, thank you!

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Created Jun 22, 2018 01:42:15

I think this is right, ISIS is usually used in the ISP network.
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Created Dec 24, 2018 01:25:44

Very helpful
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