Mutual redistribution loops

[carl_townshend]

Hi Guys

I remember seeing a good post and diagram how a loop caused by mutual redistribution between 2 routing protocols was caused and mitigated, had anyone got a good example of this with a diagram? I think it was stopped using tags or distribute lists.

Cheers

Carl

[balaji.bandi]

You can look : KB  - there are some examples provided

https://community.cisco.com/t5/networking-knowledge-base/tkb-p/4461-docs-network-infrastructure

One give example  with slides here : (hope if you look at the user posted have other examples also can be find in KB pages)

https://community.cisco.com/t5/networking-knowledge-base/routes-redistributions-slides/ta-p/4650866

[MHM Cisco World]

I study it in CCNP 
I will share the exmaple 
TroubleShooting Route RedistribuTion with Multiple RedistribuTion Points | Best Cisco CCNA CCNP and Linux/CentOS PDF Notes (ccnaccnplinux.com)

[Elliot Dierksen]

In production networks I would say that mutual redistribution is something to be avoided at almost any cost because it has so much disaster potential. I find that people think every router in a network needs every route, but that isn't the case. It needs to be able REACH everywhere, but it doesn't need every route. Looking at summarization instead is safer and more reliable.

[MHM Cisco World]

You are 100 % right, 
I think he study some Cisco Course not want to run it in real network 
thanks 

[carl_townshend]

Hi there

What would the alternative be ? if we need to get routes between 2 different networks with different protocols, how can we get around it ?

also how would summarising solve it?

[Joseph W. Doherty]

---

@carl_townshend wrote:

Hi there

What would the alternative be ? if we need to get routes between 2 different networks with different protocols, how can we get around it ?

also how would summarising solve it?

---

Somewhat like what we often do for for the Internet.

You create a static, or statics, in each AS that covers the address block(s) used by the other AS, pointing to your egress link(s) to the other AS.  Those statics are redistributed into just their local AS.

Each AS would "know" of the address block(s) within the other AS, and how to reach it, but the two ASs do not share routes, i.e. there is no route redistribution between them.

This approach has advantages and disadvantages vs. mutual redistribution.

If you do go the mutual redistribution approach, as noted in other replies, you can tag routes redistributed into the other AS while excluding accepting routes with your tag(s) coming from the other AS.

[MHM Cisco World]

one way of summary using static to Null0 to avoided mutual redistribution 
R1
router ospf 100
log-adjacency-changes
network 1.1.1.1 0.0.0.0 area 0
network 100.0.0.0 0.0.0.255 area 0
network 200.0.0.0 0.0.0.255 area 0

R2
router eigrp 110
network 110.0.0.0 0.0.0.255
redistribute static metric 100 100 255 1 1500
!
router ospf 100
log-adjacency-changes
network 100.0.0.0 0.0.0.255 area 0
ip route 1.0.0.0 255.0.0.0 Null0

R4

router eigrp 110
network 110.0.0.0 0.0.0.255
network 210.0.0.0


D EX 1.0.0.0/8 [170/25628160] via 110.0.0.2, 00:01:33, FastEthernet2/1
110.0.0.0/8 is variably subnetted, 2 subnets, 2 masks
C 110.0.0.0/24 is directly connected, FastEthernet2/1
L 110.0.0.4/32 is directly connected, FastEthernet2/1
210.0.0.0/24 is variably subnetted, 2 subnets, 2 masks
C 210.0.0.0/24 is directly connected, FastEthernet3/1
L 210.0.0.4/32 is directly connected, FastEthernet3/1

[paul driver]

Hello
I would say the filtering on tags is a good option.


Example:   At the two distribtution points:

route-map ospf-into-eigrp deny 10
match tag 110

route-map ospf-into-eigrp pemit  99
set tag 110

route-map eigrp-into-ospf deny 10
match tag 170

route-map eigrp-into-ospf pemit 99
set tag 170

router ospf x
redstribute eigrp route-map eigrp-into-ospf subnets

router eigrp x
redstribute ospf route-map ospf-into-eigrp  metric 1 1 1 1 1

[Richard Clayton]

Hi Paul

I use this method all the time in live networks and it works good

Rick