Routing Assistance

[gboyce]

Hi Folks,
I need some routing assistance if you will. I have no routing education but I have been tasked with it anyway.
I have included a network diagram that shows how things are currently.
The routing statements in our router(ASR1002x xxx.xxx.120.1) are
0.0.0.0 0.0.0.0 ourBGPaddress
xxx.xxx.121.0 255.255.255.0 xxx.xxx.120.2
xxx.xxx.122.0 255.255.255.0 xxx.xxx.120.2

We have most of our fiber customers on SW2 (xxx.xxx.120.2). Until recently each fiber customer has come to us on a fiber pair. Our fiber carrier said that this is too expensive and delivered
a new fiber pair for an NNI for all new fiber customers to go through. We want to have that NNI go into SW1 (xxx.xxx.120.4).
I tried changing the static routes in our router from the above two statements to
xxx.xxx.121.32 255.255.255.224 xxx.xxx.120.2
xxx.xxx.121.64 255.255.255.224 xxx.xxx.120.2
xxx.xxx.121.96 255.255.255.224 xxx.xxx.120.2
xxx.xxx.121.128 255.255.255.224 xxx.xxx.120.2
xxx.xxx.121.160 255.255.255.224 xxx.xxx.120.2
xxx.xxx.121.192 255.255.255.248 xxx.xxx.120.2
xxx.xxx.121.200 255.255.255.252 xxx.xxx.120.2
xxx.xxx.121.208 255.255.255.240 xxx.xxx.120.2
xxx.xxx.121.248 255.255.255.248 xxx.xxx.120.2
xxx.xxx.121.232 255.255.255.248 xxx.xxx.120.2
xxx.xxx.121.240 255.255.255.248 xxx.xxx.120.2
xxx.xxx.122.0 255.255.255.224 xxx.xxx.120.2
xxx.xxx.122.32 255.255.255.248 xxx.xxx.120.2
xxx.xxx.122.64 255.255.255.240 xxx.xxx.120.2
xxx.xxx.122.80 255.255.255.252 xxx.xxx.120.2
xxx.xxx.122.40 255.255.255.248 xxx.xxx.120.4
xxx.xxx.122.47 255.255.255.252 xxx.xxx.120.4

Both switches have 0.0.0.0 0.0.0.0 xxx.xxx.120.1
When I remove the 2 existing routing statements and put in the new ones and move the NNI to SW1 none of the fiber customers can get to the internet. I am on the xxx.xxx.120.0 network and can get to each of their devices.
I hope that someone here can point me in the right direction.

[Jon Marshall]

Okay, so leave those routes in and just add the new ones because a router will always choose the more specific route so your /27's will be used before either of the two original routes. 

And by leaving them there you will continue to advertise those two class C networks to your upstream provider. 

Jon

[gboyce]

Okay, So the new routes for the NNI will work and the customers in SW2 will continue working? Do I also need to change the path cost for any of the routes?

[Jon Marshall · Accepted solution]

Looking at the routes again you are still sending most of the subnets to 120.2 so I would not bother with those routes. 

Just leave the two original routes pointing to 120.2 and just add any specific routes for subnets going to 120.4 which means your subnets get advertised to your provider and all traffic goes to 120.2 unless you have a more specific route pointing to 120.4. 

As far as I can see that should do what you want. 

Jon

[gboyce]

Just a thought.. 

Would it be better to route all traffic to 120.4 then put routes in 120.4 to route the subnets for 121 and 122 that are in 120.2 to 120.2?

so..

router:

x.x.121.0 255.255.255.0 192.40.120.4

x.x.122.0 255.255.255.0 192.40.120.4

SW1 (120.4):

0.0.0.0 0.0.0.0 x.x.120.1

xxx.xxx.121.32 255.255.255.224 xxx.xxx.120.2
xxx.xxx.121.64 255.255.255.224 xxx.xxx.120.2
xxx.xxx.121.96 255.255.255.224 xxx.xxx.120.2
xxx.xxx.121.128 255.255.255.224 xxx.xxx.120.2
xxx.xxx.121.160 255.255.255.224 xxx.xxx.120.2
xxx.xxx.121.192 255.255.255.248 xxx.xxx.120.2
xxx.xxx.121.200 255.255.255.252 xxx.xxx.120.2
xxx.xxx.121.208 255.255.255.240 xxx.xxx.120.2
xxx.xxx.121.248 255.255.255.248 xxx.xxx.120.2
xxx.xxx.121.232 255.255.255.248 xxx.xxx.120.2
xxx.xxx.121.240 255.255.255.248 xxx.xxx.120.2
xxx.xxx.122.0 255.255.255.224 xxx.xxx.120.2
xxx.xxx.122.32 255.255.255.248 xxx.xxx.120.2
xxx.xxx.122.64 255.255.255.240 xxx.xxx.120.2
xxx.xxx.122.80 255.255.255.252 xxx.xxx.120.2

SW2:

0.0.0.0 0.0.0.0 x.x.120.4

[Jon Marshall]

You could do that but not sure what you gain by it except an extra hop for the subnets on 120.2. 

Up to you really. 

Jon