Routing Issues on Point-to-Point T1 with Cisco 1721s

[batocaster]

I am having difficulty routing traffic between two networks connected by a point-to-point T1. I am using two Cisco 1721 routers with T1 WICs. I cannot ping devices on either network across the T1. However, I am able to ping certain devices from the interface of either router. For example, when logged into router A, I am able to ping each of the interfaces of router A and router B but cannot ping beyond fa 0 on router B. When logged into router B, I can ping the interfaces of router A or router B but cannot ping beyond fa 0 on router A. Basically, I’m limited to pinging router interfaces and can’t ping beyond to the remote networks.

The T1 is supplied by a local Telco and is running ESF/B8ZS with no clocking provided by the telco. I am using HDLC encapsulation. I have my clock set to internal on router A and to line on router B. I have enabled routing on both A and B using the “ip routing” command. I am also using the Cisco Configuration Builder and have reviewed several posts which show similar configurations. I think I’m close but am still having problems for some reason.

To troubleshoot the routing issue, I have changed the static routes to point to the IP of the serial ports of the next hop for each router instead of s0. It made no difference in the configuration. If the interfaces ARE configured correctly and I have enabled “ip routing” could there be another setting I’m missing to enable routing?

I am also receiving several errors on both routers serial ports and on the service modules (T1 WICs). I have connectivity on the T1 but is it possible that my configuration is correct and that the telco’s T1 has issues? When the T1 was first installed the telco had both ESF and AMI enabled. The line did not work until they removed the AMI. Now the line protocol is up but there are several errors on the WICs and serial interfaces. The telco assures me they are not part of the problem but have also indicated they still see some AMI type traffic on the line. I am set for ESF and B8ZS, so I don't think I could be generating this unless I have a malfunctioning unit.

Sorry for the lengthy post but I thought I would drop all the info from both routers onto the site for better analysis. I am looking for a confirmation that I am configured correctly in regards to routing and to see if anyone else has resolved similar issues with errors on a T1 circuit. Any assistance would be greatly appreciated!

Router A:
version 12.3
!
ip subnet-zero
!
interface FastEthernet0
ip address 10.147.0.254 255.255.0.0
speed auto
full-duplex
!
interface Serial0
ip address 192.168.0.1 255.255.255.252
service-module t1 clock source internal
!
ip classless
ip route 0.0.0.0 0.0.0.0 Serial0
no ip http server


Router B:
version 12.3
!
ip subnet-zero
!
interface FastEthernet0
ip address 10.101.0.254 255.255.0.0
speed auto
full-duplex
!
interface Serial0
ip address 192.168.0.2 255.255.255.0
no fair-queue
!
ip classless
ip route 0.0.0.0 0.0.0.0 Serial0
no ip http server



Router A Service-Module Errors:

Total Data (last 91 15 minute intervals):
35188 Line Code Violations, 7233 Path Code Violations
1 Slip Secs, 6355 Fr Loss Secs, 6626 Line Err Secs, 242 Degraded Mins
297 Errored Secs, 11 Bursty Err Secs, 6355 Severely Err Secs, 0 Unavail Secs
Data in current interval (223 seconds elapsed):
0 Line Code Violations, 0 Path Code Violations
0 Slip Secs, 0 Fr Loss Secs, 0 Line Err Secs, 0 Degraded Mins
0 Errored Secs, 0 Bursty Err Secs, 0 Severely Err Secs, 0 Unavail Secs



Router B Service-Module Errors:

Total Data (last 96 15 minute intervals):
39872 Line Code Violations, 7601 Path Code Violations
1 Slip Secs, 6934 Fr Loss Secs, 7171 Line Err Secs, 285 Degraded Mins
347 Errored Secs, 32 Bursty Err Secs, 6851 Severely Err Secs, 83 Unavail Secs
Data in current interval (533 seconds elapsed):
0 Line Code Violations, 0 Path Code Violations
0 Slip Secs, 0 Fr Loss Secs, 0 Line Err Secs, 0 Degraded Mins
0 Errored Secs, 0 Bursty Err Secs, 0 Severely Err Secs, 0 Unavail Secs


Router A Serial0 Errors:

Serial0 is up, line protocol is up
Hardware is PQUICC with Fractional T1 CSU/DSU
Internet address is 192.168.0.1/30
MTU 1500 bytes, BW 1544 Kbit, DLY 20000 usec,
reliability 255/255, txload 1/255, rxload 1/255
Encapsulation HDLC, loopback not set
Keepalive set (10 sec)
Last input 00:00:05, output 00:00:08, output hang never
Last clearing of "show interface" counters 04:07:07
Input queue: 0/75/0/0 (size/max/drops/flushes); Total output drops: 0
Queueing strategy: weighted fair
Output queue: 0/1000/64/0 (size/max total/threshold/drops)
Conversations 0/1/256 (active/max active/max total)
Reserved Conversations 0/0 (allocated/max allocated)
Available Bandwidth 1158 kilobits/sec
5 minute input rate 0 bits/sec, 0 packets/sec
5 minute output rate 0 bits/sec, 0 packets/sec
3796 packets input, 236291 bytes, 0 no buffer
Received 1735 broadcasts, 0 runts, 0 giants, 0 throttles
0 input errors, 0 CRC, 0 frame, 0 overrun, 0 ignored, 0 abort
3677 packets output, 216711 bytes, 0 underruns
0 output errors, 0 collisions, 0 interface resets
0 output buffer failures, 0 output buffers swapped out
0 carrier transitions
DCD=up DSR=up DTR=up RTS=up CTS=up


Router B Serial0 Errors:

Serial0 is up, line protocol is up
Hardware is PQUICC with Fractional T1 CSU/DSU
Internet address is 192.168.0.2/24
MTU 1500 bytes, BW 1544 Kbit, DLY 20000 usec,
reliability 255/255, txload 1/255, rxload 1/255
Encapsulation HDLC, loopback not set
Keepalive set (10 sec)
Last input 00:00:00, output 00:00:00, output hang never
Last clearing of "show interface" counters never
Input queue: 0/75/0/0 (size/max/drops/flushes); Total output drops: 0
Queueing strategy: fifo
Output queue: 0/40 (size/max)
5 minute input rate 0 bits/sec, 0 packets/sec
5 minute output rate 0 bits/sec, 0 packets/sec
3854 packets input, 228738 bytes, 0 no buffer
Received 1862 broadcasts, 0 runts, 0 giants, 0 throttles
8426 input errors, 87 CRC, 8294 frame, 0 overrun, 0 ignored, 45 abort
11118 packets output, 422044 bytes, 0 underruns
0 output errors, 0 collisions, 2387 interface resets
0 output buffer failures, 0 output buffers swapped out
3 carrier transitions
DCD=up DSR=up DTR=up RTS=up CTS=up

 

[Enable]

Just a quick note....... you have different subnets on your serial interface they should be the same. On router A you have 255.255.255.252 and on router B you have 255.255.255.0.... Hope this helps.

-Enable

 

[batocaster]

Whoops! I have adjusted for my error in router B's subnet mask. Unfortunately, I am still experiencing the same difficulty in pinging devices beyond each router's ethernet interface.

 

[jimmyzz]

Have the devices you are trying to ping been configured with the correct default gateways? The pings may be going out, but not know how to return.

JimmyZ

 

[batocaster]

jimmyzz,

I think this might be my problem. Both 1721s are behind a firewall which is behind another Cisco router. My network looks like this:

ISP -> Cisco 2501 -> Firewall ->Router A -> point-to-point T1 -> Router B

* Router A and B were recently added to the configuration to connect a new building via a leased T1 circuit. Prior to this my setup was simply the 10.147.x.x NAT behind the firewall. The information in my post above shows the ip scheme of each interface.

The firewall provides the internal NAT and all devices on the 10.147.x.x network point to the gateway address of the firewall which is 10.147.0.1. The fa 0 address of the firewall is 10.147.0.254. I am now assuming that pings coming from the 10.101.x.x network behind router B cannot return to the 10.101.x.x network because the gateway address of the devices is pointing to 10.147.0.1 instead of 10.147.0.254 – is this correct?

If this is the case, what am I missing that would allow traffic from the 10.147.x.x network back to the 10.101.x.x network. If I change the gateway address of the devices on the 10.147.x.x network to point to router A instead of the firewall, they will not be able to access the Internet. I realize this is probably a low-level question but I am new to routing, so any assistance is appreciated.

Thanks,

batocaster

 

[IllegalOperation]

I might be missing something here, and I might be wrong....but dont you need to add some more configurations to your serial interfaces?

Considering we are talking about point to point T1s, the first thing I noticed is you dont even have the dlci identified on neither interface. As far as encapsulation goes, dont you have to use the same method your telco provider is using? I thought the most common was frame relay (IETF), and not HDLC. I know the lmi type is set to autosense by default, but I never trust that feature (I usually statically assign the lmi). Whatever the case, I could have sworn the DLCI information is needed on each interface.






If I am wrong about that part, then simply disregard all of it - and try this....


Router A:
ip route 10.101.0.0 255.255.0.0 192.168.0.2

Router B:
ip route 10.147.0.0 255.255.0.0 192.168.0.1


That should work. Let me know what happens when you do that...

 

[Cluebird]

Have you confirmed your controller settings for the WICs? I don't see the timeslots specified. After that, try clocking both ends from the line.

Also, make sure your provider isn't using bit-robbed signalling since the 1700s only support a speed of 64.

interface Serial0/0
ip address 10.0.0.51 255.0.0.0
service-module t1 framing esf !default
service-module t1 linecode b8zs !default
service-module t1 timeslots 1-12 speed 64 !missing
service-module t1 cablelength short 440ft !tweak for attenuation

After the controllers are working correctly on the lines, then take care of L3.

Since you're not running frame-relay, the DLCIs and IETF are irrelevant. HDLC should work since you're connecting to Cisco devices. Otherwise, PPP.

 

[Cluebird]

Forgot to mention. After changing the controller information, reload the boxes.

 

[Enable]

Ok is your serial interface a T1 CSU/DSU, if so you have to enable the timeslots to use.

so you have to type the following command in your interfaces.

config t
interface s0
service-module t1 timeslots 1-24


Let me know if this helps....

 

[batocaster]

Thanks to all who assisted. I am up and running. My first issue was the subnet on serial interface. The service-module was also pre-set for 24 timeslots (I’m guessing this is the default?) My other problem was that my firewall had to be set to route to the 10.101.x.x network via router A’s fast-ethernet port. This is what was preventing the pings from being returned. Again, thanks for everyone’s input. It is appreciated!