Eigrp - How to modify Admin distance for redistributing connected links and over WAN

[popularbhaskar]

We have a single EIGRP domain 101 across 2 locations (A and B) separated by a WAN link. Each location has a number of L3 switches at the IDF behind the router which has  the L3 vlans VL1, VL2 etc. We run eigrp 101 across all the switches and on the routers but we dont advertise any of the L3 vlans on them and we do redistribute static and connected for the static and the vlans to be distributed on eigrp.

Qn

1. How do i reduce the admin distance of the directly connected vlan on IDF on our core switch. ie. Vl1 and Vl2 that are distributed via connected has a admin distance of 170 locally as the other switches sees that as External without having to advertise the networks individually on each switch.  

2. Is that possible to increase the admin distance over the WAN link without having to create a 2nd eigrp domain. ie.. Add a admin distance of say 50 over the WAN link  and that way devices on both sides do see that there is a 130 distance for the remote side and 90 for local for admin distance.

Why?
I am trying to separate two locations and i don't think we will be able to create an additional domain and i am trying to see alternate methods of achieving this.  

Additional info-

The design i mentioned has 2 locations with a WAN connection and i have mixed (90/170) distance based on where the routes are coming(eigrp/connected/static) from eventhough  everything is within the same network.  We only have 1 Eigrp network 101 and was looking to alter the AD for just connected if at all possible.

Assuming i put in all the routes into the network how can i make site 2 see the site 1 network with a larger admin distance and 1 to 2 with a larger admin distance while not altering the admin distance within the local site.

Underlying reason: We are getting a MPLS link(lower bandwidth) connecting to site 3,4 and 5 at both sites and wanted to clear the internal routing first before i can add them or redistribute them into bgp.

[paul driver]

Hello

You can manipulate incoming eigrp external route distances on each router with the following command example:

"Note: this example just shows one side of the configuration but you will need to perfrom this on each router and also notice the eigrp adjacency resets when you change the admin distances!"

rtr#sh ip route  eigrp

D EX 1.0.0.0/8 [170/409600] via 10.1.12.1, 00:00:04, FastEthernet0/0
D EX 111.0.0.0/8 [170/409600] via 10.1.12.1, 00:00:04, FastEthernet0/0
D EX 11.0.0.0/8 [170/409600] via 10.1.12.1, 00:00:04, FastEthernet0/0

router eigrp 12
distance eigrp 90 130

rtr#
*Mar  1 00:19:31.223: %DUAL-5-NBRCHANGE: IP-EIGRP(0) 12: Neighbor 10.1.12.1 (FastEthernet0/0) is down: route configuration changed

rtr#
*Mar  1 00:19:32.731: %SYS-5-CONFIG_I: Configured from console by console
*Mar  1 00:19:33.511: %DUAL-5-NBRCHANGE: IP-EIGRP(0) 12: Neighbor 10.1.12.1 (FastEthernet0/0) is up: new adjacency

rtr#sh ip route  eigrp

D EX 1.0.0.0/8 [130/409600] via 10.1.12.1, 00:00:32, FastEthernet0/0
D EX 111.0.0.0/8 [130/409600] via 10.1.12.1, 00:00:32, FastEthernet0/0
D EX 11.0.0.0/8 [130/409600] via 10.1.12.1, 00:00:32, FastEthernet0/0

res

Paul

[popularbhaskar]

Paul,

  Would the devices behind the router have the admin distances as 130 also as i thought the admin distance is just for that device.

ie. switch 1A, 1B,1C are behind router 1 and switch 2A 2B and 2C are behind rotuer 2. The WAN connects router 1 and 2. If we ran router eigrp 12 distance eigrp 90 130 on router 1 and router 2.

The switches behind router 1 - would see the local routes with AD 90 and the routes through the wan as AD 130.

The switches behind router 2- would see the local routes with AD 90 and the routes through the wan as AD 130.

Keep in mind its a single eigrp domain.

Is my assumption right?

[paul driver]

Hello

"as i thought the admin distance is just for that device."  - Your assumption is correct- 

Take R1 for instance -The routes received on R1 from R2 with the config I have shown will decrease the admin distance to 130 ONLY on R1 , The routers BEHIND R1 will still receive the external routes from R2 with admin distance of 170 - unless you do the same on those routers instead of R1 itself.

Hope this is clear?


res

Paul

[popularbhaskar]

Thank you paul and Jon!  Truly appreciate your response.

   I think i now know what to do.  We have L3 at IDF and the issue is that we are not advertising those networks on eigrp and instead they are learning it as connected routes and hence the 170.

I am going to plan on advertising all the networks through eigrp to make things uniform.

One last qn..

Can you provide an example as to how we can redistribute the eigrp routes into bgp. My peer sites run ospf and bgp for mpls and we dont run ospf and run just eigrp and we need to redistribute our eigrp routes into the bgp and learn the bgp routes into eigrp as we are getting the mpls at both of our sites?

FYI.. The reason why i was worried about AD is as the redistribution will make the locations use the MPLS instead of the direct WAN P2P.

[Jon Marshall · Accepted solution]

If these two sites are connected via a P2P link and you are exchanging EIGRP routes across it then you need to be aware of what you redistribute into BGP because each site will know about it's own subnets but also the other sites subnets.

If you just redistribute all EIGRP at both sites then it's a lottery as to which MPLS connection the non EIGRP sites use.

So you either need to -

1) when you redistribute EIGRP at each site into BGP use a route map and only allow the local networks for that site

or

2) if you want each of the EIGRP sites to back each other's MPLS connection up you could have them both advertise out all networks ie. their own and the other EIGRP site's networks but modify the BGP attributes of the non local networks so they are least preferred.

You still want to use a route map to ensure only the local and other EIGRP sites network are redistributed because remember you are also receiving BGP routes from the non EIGRP sites and redistributing these into EIGRP at each site and these are exchanged via the P2P link as well.

It realty depends on what you are trying to do.

The actual basic redistribution is very straightforward, see this link -

http://www.cisco.com/c/en/us/support/docs/ip/border-gateway-protocol-bgp/113506-failover-eigrp-bgp-00.html

but you need to decide what you are going to do in terms of EIGRP to BGP advertisements as covered above.

I'm not trying to make things complicated for you but because you have a P2P link connecting these sites and you are running EIGRP over it then any routes received via BGP will be redistributed into EIGRP and you need to make sure they are then not redistributed back into BGP on the other site router.

Jon

[Jon Marshall · Accepted solution]

An alternative solution which would reduce the complexity is to only do redistribution from BGP to EIGRP.

Then you use "network ..." statements under your BGP configuration to advertise your local site networks.

You may even be able to configure a summary route and just advertise that.

If you only do one way redistribution you do not need to worry about filtering any routes going back into BGP.

Depends on the amount of subnets you have at each site but could be an option.

Jon

[popularbhaskar]

Thank you so much for your help! Truly appreciate it.

[popularbhaskar]

Thank you so much for your help! Truly appreciate it.

[paul driver]

Hello

Another alternative I think my be applicable if I understand your last query is to run bgp and eigrp in parallel

Advertising your local routes in bgp AND eigrp so the other side will see two paths to the same destination - obviously bgp with the lower admin distance would be proffered over the direct P2Ppath of eigrp.

However you can manipulate this also with a bgp command called backdoor which will make the bgp path least proffered and use the more direct path over eigrp.

It actual a locally specific command so you need to run it on site A and B and it increases the route to a admin local distance of 200
 

example:
remote B site router sees 1.1.1.1 via ebgp with a admin distance of 20

on this router:
router bgp xxx
network 1.1.1.1 mask 255.255.255.0 backdoor

Now remote B site router sees 1.1.1.1 via eigrp with a admin distance of 170

res

Paul

[Jon Marshall]

You can manipulate the AD if needed but it's not clear, to me, what the issue is.

Are you saying you are using the same IP subnets at each site ?

If they are then as both sites are redistributing connected the WAN link would increase the metric so the local routes would be preferred.

If they aren't then you would want routing between the sites I would have thought.

If Paul's suggestion works for you then please ignore but it's not clear what the actual issue is.

Jon