Auto-failover 2600 MX Record between T1 and DSL

[4DeanB]

Thanks for reading this post. I have a 2610 with S0/0 connected to a 1.5M frame-relay Internet T1 on a /30. The same provider gave us a /28 block of which the first usable is currently assigned to e0/0 and the second usable is set on the WAN side of a firewall/email appliance connected to e0/0. The customer's email MX record is pointed at the WAN side of the appliance. The customer installed a DSL including 5 static IP addresses with the idea of having an alternate back-up circuit available for Internet and email access in the event the Internet T1 dies. I spoke with the people hosting their MX record and they can set weighted addresses to send the mail to one address or another if one should fail to respond. How can I configure the 2610 to utilize the T1 for everything always except in the event the T1 dies, swing all Internet traffic to e0/1 set to one of the DSL statics? AND have the email routed inbound to the same firewall/email appliance WAN address? AND outbound email be routed out the DSL as well? AND switch back to the T1 when the T1 comes back up?


DNS Host:
send email to 12.1.1.2 /28
unless down then
send email to ?



ISP B ISP A
DSL router LAN 65.1.1.1 /29 |
| |
|-----------e0/1-- 2610 --s0/0
65.1.1.2 /29 |
|
e0/0 12.1.1.1 /28
|
firewall/email box WAN=12.1.1.2 /28
| LAN=192.168.1.1 /24
|
Local network
192.168.1.X

 

[pmesjar]

Have you considered using administrative distances in static routes set up on 2610? IP route syntax:

ip route DESTINATION MASK OUTGOING-INT/NEXT-HOP-IP <admin-distance>

where admin-dist can be a number from 1 to 255 and is like a degree of preference amoung various protocols router learned about this route (EIGRP has 90, OSPF has 110, RIP has 120, etc). By default static routes are created with admin distance 0 if you point it to outgoing-int and with admin distance 1 if you point it to next-hop-ip.

I do not know if you are using any dynamic routing with the providers, but my strong guess is that you are using BGP over Frame Relay (almost 95% sure). You might try following concept:

If you are not running BGP, ask the provider ISPA to set up Exterior BGP session (eBGP) with your 2610, but tell him you want only default route to be sent to your 2610 router. In your 2610 router you will have BGP route record with address 0.0.0.0/0 and admin-distance of 20. Then you can set up another static default route on your 2610 pointing to ISPB with higher admin-distance,eg:

ip route 0.0.0.0 0.0.0.0 NEXT-HOP-IP-ISPB-ROUTER 100

this way while your Frame Relay circuit will be up, everything will go via this link. When it goes down, DSL line will come up almost instantly. When the Frame Relay comes back up, the static route will be removed from routing table (but stays in your config.

The concept I have presented is also known as floating static routes, maybe you've heard about it. Hope this helps

Peter Mesjar
CCNA, A+ certified
pmesjar@centrum.sk