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Inter and Intra routing

DR Diag.png

Branch is connected to headoffice and DR site . It has got multiple tunnels one pointing to HO and other pointing to DR .

When we check Headoffice ( WAN 2 router ) for show ip route 192.168.18.0 which is branch IP it shows that route is getting learned from direct tunnel and route is considered as intra area . It shows Intra area because the outside interface is advertised with area 300 even though the inside is in area 0 . This makes WAN 2 work as ABR .

However when I do show ip route 192.168.18.0 from WAN 1 it shows route as Inter area because that route is getting learned from WAN 2 inside interface so both becomes area 0 .

DR link from DR to HO and terminated that on WAN 1 . Aim is that if WAN1 and WAN2 links fail then branch should be accesiable through DR link . Routing is configured for DR to HO however when I do show ip route 192.168.18.0 on WAN 1 it starts learning routes from DR as first priority ( Intra area ) while my aim was to get it learned from Headoffice link ( considered as Inter area for other devices and intra area for WAN 2 ) . Only if Headoffice link fails then it should learn through DR

Any comments ?

5 REPLIES

Inter and Intra routing

Hi,

Without know much about the link type/bw, I guess ospf using default cost caliculation. One way of manipulating the metric is to use ip ospf cost bet WAN1 & DR (interface level).

Thx

MS

Inter and Intra routing

increase the ip ospf cost on interface. ( set the Lower value of IP ospf cost on DR router towards WAN1 link). So it will take the first path as  Head Office(WAN2) router.. If WAN 2 fails.. it will go for DR..( also reduce  ospf cost b/w WAN2 & WAN 1)

Cisco Employee

Inter and Intra routing

Gentlemen,

I do not believe that increasing costs on interface will help here.

The original poster has indicated that the 192.168.18.0/24 is learnt as intra-area route on WAN1. Because OSPF strictly prefers intra-area routes to inter-area routes, changing the link costs is useless.

I wonder, however, how is it possible that WAN1 router learns about this network as an intra-area route. That would mean that WAN1 router already has a link in the area 300 and is also an ABR. That, however, contradicts what the original poster had indicated earlier: "However when I do show ip route 192.168.18.0 from WAN 1 it shows route  as Inter area because that route is getting learned from WAN 2 inside  interface so both becomes area 0 . "

Perhaps the original poster can clarify this better. In any case, a better topology picture would be helpful. In particular, I would like to see the individual tunnels and OSPF adjacencies between routers including better information about areas and their boundaries.

Best regards,

Peter

New Member

Inter and Intra routing

I've to agree with Peter that a better topology and tunnel's configuration should be nice to have and to understand well the situation.

     Things to consider: tunnels type, ospf adj,

as advice to the design you should consider create an second link between HO and DR via WAN2.

Best Regards,

Alcides MIguel

New Member

Re: Inter and Intra routing

Here is a revised diagram . Even though WAN 1 has tunnels to other branches I have removed link in this latest diagram as it will create confusion and those tunnels are not related to this problem .

Branch communicates to WAN 2 using tunnel

Branch communicates to DR Site using tunnel


This issue is not related to ospf cost , it is related to inter and intra area routes . If i connect DR link to WAN 2 rather than WAN 1 then things would become fine as both routes would be of same type and selection would be done using metric calculation .

However due to some limitations I have to terminate this link on some other device i.e. WAN 1 or Switch ( below drawn ) .

In current case if I change DR from area 300 to area 0 would it be helpful ?

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