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Routing loop redistributing a longer prefix static route

I have what seems a simple problem and I must be overlooking a simple solution.

Please see the attached diagram for details. I have 3 typical routers all successfully participating in a single EIGRP process. Currently, all traffic flows through the higher bandwidth connections as it should. My goal is to have all traffic from a single host A to single host B go a different route via the T1.

All this is shown in my attached diagram. I am trying to make this traffic flow change by creating a static route in Router B which is redistributed into EIGRP.

The problem is a routing loop is formed because Router C thinks that the more specific route is at Router A when it really is on its local Connected interface.

How can I have Router C ignore/overcome the more specific route to Host B and use its connected interface? I am open to a better way to make this happen, too.

I have tried a distribute-list out filter at Router A to stop the advertisement of the static route (within EIGRP). This did not work because Router C now has a route back to Router B for the more specific route. (Note: this is not indicated in the diagram)

7 REPLIES

Re: Routing loop redistributing a longer prefix static route

Your eigrp metrics are defaults - it will prefer the 100mbs every time.

Do you just want 1 host or all hosts to go over the T1?

New Member

Re: Routing loop redistributing a longer prefix static route

Just the 1 host while all other traffic is unaffected.

Re: Routing loop redistributing a longer prefix static route

Just as Jon has suggested - PBR is the way forward.

Hall of Fame Super Blue

Re: Routing loop redistributing a longer prefix static route

If you want to send just traffic for one host a different way then there are 2 easy options

1) add a static route to both A & B for the host specific route.

2)Use Policy Based Routing (PBR) on both A & B.

Note that return traffic will still go from C -> A. If you want return traffic to go back via B then you definitely need PBR.

Jon

New Member

Re: Routing loop redistributing a longer prefix static route

In the end I do want return traffic to go via B so it looks like PBR is the way to go.

I am just surprised that a connected route would not override an externally learned route even if it has a more specific prefix.

Can you give me a sample of what the PBR would look like? I have not done a PBR before.

Hall of Fame Super Blue

Re: Routing loop redistributing a longer prefix static route

Traffic to 10.157.10.4

======================

On router A

-----------

access-list 101 permit ip any host 10.157.10.4

route-map to-B-C permit 10

match ip address 101

set ip next-hop

int fa0/0 (interface of LAN on router A)

ip policy route-map to-B-C

On router B

-----------

access-list 101 permit ip any host 10.157.10.4

route-map to-C permit 10

match ip address 101

set ip next-hop

int fa0/0 (interface connecting router B to router A)

ip policy route-map to-C

Traffic from 10.157.10.4

========================

On router C

-----------

access-list 101 permit host 10.157.10.4 any

route-map to-B-A permit 10

match ip address 101

set ip next-hop

int fa0/0 (interface of LAN on router C)

ip policy route-map to-B-A

On router B

-----------

accesss-list 102 permit host 10.157.10.4 any

route-map to-A permit 10

match ip address 102

set ip next-hop

int ?? (interface connecting router B to router C)

ip policy route-map to-A

Note - I have used "any" in all the access-lists. This means that all traffic

to and from the host 10.157.10.4 will take the long path. if you want to narrow

that down to just the LAN hanging off router A replace "any" with the subnet/reverse

mask of the LAN A in the acls.

Jon

New Member

Re: Routing loop redistributing a longer prefix static route

Thanks, I'll give this a try.

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