WAN Migration

[dervish]

Using a Cisco 3640 with 2 CT1 CSU cards channelized to privide 2 groups of 4 (6 channels each X 64K=384K)internet access via point to point T1's to the various location. Originally using Wic-1dsu for ISP's T1. The objective was to add an additional Wic-1dsu for a new ISP in order to simplify migrating from the original T1 ISP to the new T1 ISP.

After adding the ip routing info for the new ISP, several of the remote locations appeared to be working correctly. However; when I shutdown or unplug the original T1 to the original ISP, internet access stops, although I can still I ping and telnet the various remote gateway routers. The circuit is known good, as I can plug in an Adtran 608 (non-channelized) and the internet pops right up.

Since I'm only using 1 group of 4, and the remaining channel groups are in shutdown mode I'm comfortable that it isn't a channel bandwidth problem. I've swapped positions with the Wic-1dsu cards, and the symptoms are the same, seeming to rule out the possibility of a bad dsu card. I've searched in vain for a configuration example showing a cisco using 2 Wic-1dsu Serial Wan interfaces, any help is deeply appreciated.

Essentially, any information regarding dual Wan interfaces in the Cisco environment would be helpful in solving this problem.

 

[Frenchie2069]

What do the routing tables look like on the remote and local routers? Are you sure that there is no reference to the old ISP address (or the interface connected to the old ISP)?

HTH,
Michael.

 

[dervish]

The ip addresses for the remote routers are all private ip's (i.e. 192.168.1.2, 192.168.2.2, etc...). The LAN side of each of the remote routers is either private (i.e. 172.16.1.2, 172.16.2.1, etc...) or uses a .248 subnet of the T1 ISP's public ip allocation. The references to the T1 are respectively (ip addresses excluded for obvious reasons):

(old ISP)

interface Serial0/0
description connected to Internet
ip address xxx.xxx.xxx.xxx 255.255.255.252
ip nat outside
encapsulation ppp
no ip route-cache
no ip mroute-cache
service-module t1 remote-alarm-enable
no cdp enable

(new ISP)

interface Serial0/1
description NEW ISP connection to Inet
ip address xxx.xxx.xx.xxx 255.255.255.252
ip nat outside
encapsulation ppp
no ip route-cache
no ip mroute-cache
service-module t1 remote-alarm-enable
no cdp enable

The confusing part of this is that when I issue a shutdown command (or unplug the old ISP T1) on serial0/0, I lose internet access, but I can still ping and telnet the remote routers on either their private or public ip addresses. Bare in mind that all of the remote routers are connected to to our CO via point to point T1's. We then DAC's these T1's and split off the voice portion of each circuit to our DMS phone switch, with the remaining 384K of bandwidth being split off to the channelized Cisco. Indeed, all the cisco ever sees is the group of 4 (6 channels X 64K=384K per channel group)channel groups It's been running like a hose for months, with zero down time. The Telco providing the new ISP T1 circuit has less than stellar tech support staffing (I had to show their engineers how to cable and turn on the Adtran 608), so any immediate solution from that end appears faint.

Thanks for your help
Ed

 

[longneck]

Can you do a "show ip route" on all three routers and post it here? Also post the portion of the configs on each router that deal with routing protocols.

- Carl

 

[dervish]

Sorry, but security purposes would seem to preclude my posting the routing info. That The routers all work correctly when using the "old isp" T1, and, they all seem to work correctly with the "New isp" t1 (until I shutdown or unplug the "old isp" t1) is the nub of the problem.

The fact that the routing tables are apparently working correctly when using one T1 circuit, and the fact that I can ping and telnet the various routers after disabling the "old isp" would seem to indicate that the routing tables are correct, or at least workable. Basically, the project shouldn't be any more difficult than changing the serial wan address to point to the "new ISP" t1.

I can provide a scenario of the table routing that might be helpful in understanding the simplicity of the routing involved, and my confusion that it works with one t1 and not the other.

Essentially, the Cisco is configured with 2 Wic-1dsu cards. This is the inbound/outbound path for the 2 T1 circuits involved (see Serial0/0 and Serial0/1 above).

The remote routers, connected by point to point T1 to our Central Office where the Cisco 3640 is located. The Cisco has 2 CT1 cards, channelized with 4 channel groups each, 6 64K channels per channel group, essentially providing 384K of internet bandwidth to the 4 remote locations via point to point T1's. 4 of the channel groups are diabled.

For purposes of testing, no firewalls are used.

Router #1

Wan Ip Address 192.168.1.2 255.255.255.0
Lan Ip Address 172.16.1.1 255.255.255.0

workstations attached to this router are configured with ip addresses in the range of 172.16.1.2 through .253 and use a gateway ip of 172.16.1.1. The appropriate primary and secondary DNS (depending on which T1 I'm testing) is used.
From the Cisco side, I can ping and telnet with no problem.

Router #2

Wan Ip Address 192.168.2.2 255.255.255.0
Lan Ip Address 172.16.2.1 255.255.255.0

workstations attached to this router are configured with ip addresses in the range of 172.16.2.2 through .253 and use a gateway ip of 172.16.2.1. The appropriate primary and secondary DNS (depending on which T1 I'm testing) is used.

From the Cisco side, I can ping and telnet with no problem.

Router #3

Note! the following routing table is provided as an example that uses public ip addresses on the "new isp" T1. Note that the Wan ip is still a private ip on the Cisco 3640, and, the same scenario (works with both T1's enabled, no internet with the "old isp" T1 disabled, yet I can still telnet and ping the router.

Wan Ip Address 192.168.3.2 255.255.255.248
Lan Ip Address 209.194.xxx.x93 255.255.255.248

workstations attached to this router are configured with ip addresses in the range of 209.194.xxx.x94 through .198 and use a gateway ip of 209.194.xxx.x93 The appropriate primary and secondary DNS (depending on which T1 I'm testing) is used.

When I run a trace route to the above public ip address (both T1's enabled), everything looks fine, and there are no hops that indicate connectivity to the "old isp" T1.

From the outside, it looks like there is no problem. The 15 hops indicated by the trace are exactly what I expect to see. From the Cisco side, I can ping and telnet with no problem, and from the outside (internet) I can ping, traceroute, telnet etc with no problem.

If I disconnect the "Old ISP" t1, I can still ping and telnet to Router #3, but a laptop attached to Router #3 cannot access the internet (server not found is the most commont error message). I can however ping from the Cisco to the laptop's public ip address. If I restore the "Old ISP" T1, the laptop readily accesses the internet, and syndry other tests run from the laptop don't indicate that a problems exists. Weird or what!

 

[jwi71]

Let me see if I follow you:
Regardless of which T1 is "active", you have complete connectivity within your network. Yes?
With the "old ISP" up, you can browse the internet. Right?
The "new ISP" only works with the "old ISP" plugged in. ok?

What is the last response with a trace when "old ISP" is unplugged? What does it look like from the outside (a trace into your network)?

J

 

[dervish]

Yes, that's about it.

Perhaps a faster way to achieve my objective (at least requiring fewer keystrokes) would be to pose a question instead of trying to troubleshoot my present configuration.

The question would be:

Is their an example that could be shown for the following:

A Cisco 3640 router connected to 2 different ISP T1's via 2 Wic-1DSU cards. An example using the Cisco's on-board ethernet port (I'll just use a scondary ip address for the ethernet port to allow for the "old ISP" T1, "New ISP" T1 scenario)would be all I require. Once I can prove access to the "new ISP" T1, after disabling the "old ISP" t1, I can resurrect the routing on the channelized T1's in a jiffy.

Fortunately, I won't have to take our customers down, as I have several other Cisco routers that will allow me to add an additional Wic-1DSU (although I won't be able to duplicate the channelized CT1 routing). I can thin use one of my "backup t1 circuits" in conjunction with the "new ISP" t1, and that should allow me to test by disabling one or the other of the T1's.

Does anyone have an example of this sort of configuration that they know to be working?

 

[dervish]

Ooops! I neglected to mention that all routers involved are using ppp encapsulation.

 

[longneck]

When you ping and traceroute to test internet access, where are you running those commands from and what are your pinging? Just because you can ping the IP for external interface of your new ISP doesn't mean internet access works.

Depending on how you have your routing set up, the router may not be taking those routes out of the table when you disconnect the old ISP. You can ping on the new ISP's network all you want, since that already is the preferred route.

So, what is your routing configuration?