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New Member

Redundant L3 to MPLS Router - Comments

With the diagram below as an example..  can anyone comment on the efficiency of this design, and/or a better method.

Router_with_Dual_L3.jpg

4 REPLIES
Hall of Fame Super Silver

Re: Redundant L3 to MPLS Router - Comments

Hello Dsidley,

first of all, you should remove the EIGRP stub in order to have a correct behaviour of routing over the link between L3A and L3B.

EIGRP stub implies no other routers behind and this is not your case if L3B should use the link to L3B or viceversa

I would suggest to use point-to-point routed links for connections to the WAN router.

A L2 trunk link carrying all 4 client Vlans and an additional vlan for routing is suggested.

For the L2 trunk an etherchannel is recommended and I would use LACP on the bundle.

The use of point to point routed links allows for easy tracking of the state of these L3 ports in order to decide what L3 switch is active for HSRP.

One HSRP group for client Vlan

Alternatively the use of GLBP can be considered.

using an SVI can lead to undesired effects (the SVI can be still up/up when link to WAN router fails if at least one port in STP forwarding state exists including L2 trunks)

the link WAN - L3A can be made primary to reach the client vlans IP subnets by manipulating delay on the other link WAN-L3B (by increasing it)

Hope to help

Giuseppe

New Member

Re: Redundant L3 to MPLS Router - Comments

Hi Giuseppe,

I think you are correct on the EIGRP Stub in that the L3's currently have the IPBase IOS running.

I believe with that IOS feature set I can only run EIGRP in "Stub" mode on these.

What confuses me is that I have EIGRP nei between the two L3's and also between each L3 and the associated router port (gi0/0 and gi0/1)

If I do a "sh ip eigrp topo" on either L3 switches I do see the path to the router.

On last thing is on each L3 I have "no passive" on each L3s uplink to the router.

So will the L3s advertise only the subnet they uplink to the router on, or will each L3 advertise the 4 local subnets as well?

Hall of Fame Super Silver

Re: Redundant L3 to MPLS Router - Comments

Hello Disdley,

you are right with a too "basic" feature set you have only EIGRP stub

>>So will the L3s advertise only the subnet they uplink to the router on,  or will each L3 advertise the 4 local subnets as well?

on the link to the WAN router each L3 device will advertise the 4 client Vlans.

The problem is the link between the two devices.

In a case like this I would even consider to use RIP or to upgrade to a better feature set

Hope to help

Giuseppe

Re: Redundant L3 to MPLS Router - Comments

With the diagram below as an example..  can anyone comment on the efficiency of this design, and/or a better method.

Hi,

With the objective in the diagram for simple and best use L3 A and L3 B switch a default route towards the routers interface,as you want have L3 A as active for all vlans use HSRP with making L3 A pirority as high for all vlans.so when ever traffic comes to L3 A all traffic will be routed via L3A and peer end interface of router.

Configure etherchannel between L3A and L3B as both are cisco so pagp may be prefered,but you have multiple point of failure are having in your current setup,like if your router goes down then no traffic can pass in /out and as your server are having single nic connected with L3A or L3B at this point if L3 A goes down then server connected with L3 A cannot be communcated with network unless a manual intervention from administrator.

so if possible to avoid breakage at server level try to have dual nic connecting with two different switches with teaming configured at server level.

Hope to Help !!

Ganesh.H

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