Strange problem with ASR1001-X

[gasparmenendez]

Hi folks, I've been always working with an ISP, let's call it A. ISP A give me IP address 208.X.X.182/30, obviously where 208.X.X.181 is my Gateway:

interface TenGigabitEthernet0/0/0
 description *** ISP A ***
 ip address 208.X.X.182 255.255.255.252

In my ASR1001-X I had this: ip route 0.0.0.0 0.0.0.0 208.X.X.181 and besides I have my own IP addressing (170.X.X.0/22) and everything was working fine.

Last week my company hired a second ISP (let's call it B). ISP B gave me 187.X.X.113/31 and Gateway 187.X.X.112:

interface TenGigabitEthernet0/0/1
 description *** ISP B ***
 ip address 187.X.X.113 255.255.255.254

So, I changed to this ip route 0.0.0.0 0.0.0.0 187.X.X.112 in the ASR and keep using my own addressing (170.X.X.0/22). Everything keeps working fine but I have a problem with interfaces showing traffic. I expect that all traffic goes through interface TenGigabitEthernet0/0/1 but I'm getting this:

Contencion1001-X#sh interface TenGigabitEthernet0/0/1 | i rate
  Queueing strategy: fifo
  5 minute input rate 0 bits/sec, 0 packets/sec
  5 minute output rate 73785000 bits/sec, 51960 packets/sec

and this:

Contencion1001-X#sh interface TenGigabitEthernet0/0/0 | i rate
  Queueing strategy: fifo
  5 minute input rate 790589000 bits/sec, 80042 packets/sec
  5 minute output rate 0 bits/sec, 0 packets/sec

my question is: should not interface TenGigabitEthernet0/0/0 shows no traffic at all ???

[chrihussey · Accepted solution]

All your traffic is going out the T0/0/1 interface, but the return traffic is coming back through the first ISPF on T0/0/0.

Either that or your second ISP is not advertising your 170.x.x.0/22 address block at all, or both ISPs are advertising your 170.x.x.0 /22 to the Internet and ISP #1 (T0/0/0) has the best return path.

Obviously, if it is the first issue, you need to get that rectified. If it is the second issue you could ask ISP #1 to AS prepend your block to the other ISPs.

Other than that you could possible BGP peer with both ISPs from the ASR1001 and control it yourself.

Hope this helps

[gasparmenendez]

many thanks!!!

definetly is the second issue, since my second provider is advertising my 170.x.x.0/22 address block. I have planned BGP in the near future but my concern would be: what happens if ISP A goes down ?? the return traffic would comes through T0/0/1 ?????

Thanks.

[chrihussey]

If you decide to BGP peer with both ISPs and your connection to either of them goes down, traffic should just reroute to the other. Since you are doing it all in one router it should be fairly simple to implement.

Appreciate the earlier votes.

[gasparmenendez]

thanks chrihussey, I understand what you say, but the question is: right now (befor BGP) if ISP A goes down the return traffic would comes through T0/0/1 ????? I mean, would I still have access to internet???

Thanks.

[chrihussey]

If the link to ISP A fails, if they are configured properly (and they should be) they should stop advertising your route to the rest of the Internet. Generally, the route to your netblock from the ISP is based on astatic route to you across the link. If that link fails the route should be withdrawn.

[gasparmenendez]

ok got it

Thanks!!