Multlink fine with 2 T1s but remove one and does not work

[jwhitecomputers]

We have two T1s to Qwest using MLPPP. When we remove a link we get Multilink up, one serial interface is up, and the other is down but we cannot send/receive internet traffic. QWest says everything is setup correctly on both ends.

We have a Cisco 3640 Router with IOS 12.2(7a)

Any help is appreciated!

[Georg Pauwen]

Hello,

can you post the configuration of your 3640 ?

Regards,

GP

[jwhitecomputers]

Should have thought of that - QWest did walk me through the config.

!

version 12.2

service timestamps debug uptime

service timestamps log uptime

service password-encryption

!

boot system flash slot0:c3640-is-mz.122-7a.bin

enable secret 5 xxxx

!

username xxxx privilege 15 password 7 xxxx

ip subnet-zero

!

!

ip name-server xx.xx.xx.xx

ip name-server xx.xx.xx.xx

!

call rsvp-sync

!

!

!

!

!

!

!

!

interface Multilink1

ip address xx.xx.xx.xx 255.255.255.252

no cdp enable

ppp multilink

no ppp multilink fragmentation

multilink-group 1

!

interface Ethernet0/0

no ip address

no ip redirects

shutdown

half-duplex

no cdp enable

!

interface Serial0/0

no ip address

encapsulation ppp

ppp multilink

multilink-group 1

!

interface Serial0/1

no ip address

shutdown

!

interface Ethernet1/0

no ip address

no ip redirects

shutdown

half-duplex

no cdp enable

!

interface Serial1/0

no ip address

encapsulation ppp

ppp multilink

multilink-group 1

!

interface Serial1/1

no ip address

shutdown

!

interface FastEthernet2/0

ip address xx.xx.xx.xx 255.255.255.224

no ip redirects

duplex auto

speed auto

no cdp enable

!

interface FastEthernet3/0

ip address xx.xx.xx.xx 255.255.255.252

no ip redirects

duplex auto

speed auto

no cdp enable

!

ip classless

ip route 0.0.0.0 0.0.0.0 Multilink1

no ip http server

ip pim bidir-enable

!

no logging trap

!

dial-peer cor custom

!

!

!

!

line con 0

line aux 0

line vty 0 4

login local

transport input telnet

!

ntp clock-period 17179876

ntp server 192.43.244.18

end

[bhatia.sachin]

Please specify encapsulation at Multilink int and change the default route to point to next hop instead of Mult. int.

[jwhitecomputers]

It won't let me add "encapsulation ppp" to the multilink. When I add it - it does not give me an error but doesn't show up on the "sh run" command.

I changed the hop and still same effect - when I unplug one T1 circuit I lose all connectivity but looks like some kind of data is bouncing around - about 50k is. When I plug it in I get the full 3m back.

[amit-singh]

Hi,

Please check with your ISP what route they are using to throw the traffic back to your network.

What happens when you ping the multilink IP when you have one T1 disconnected. It seems your second T1 is not through.

What does the interface says when you disconnect the other T1. Please paste the output of your interface.

Do one thing, unplug your one T1, ask your ISP to give you a remote loop from their end to your end and then try pinging the local IP i.e the IP of the multlink interface at your end. If you get the ping back the T1 is through.

If you dont get it then try the local loop at your end and do the testing.

HTH,

-amit singh

[jwhitecomputers]

I can ping the multilink interface on my end just fine when I unplug either T1. When both T1s are plugged in I get full 3meg bandwidth. When either one is unplugged I cannot get anything out/in to the internet.

Here is one interface when it is unplugged:

Serial1/0 is down, line protocol is down

Hardware is QUICC with integrated T1 CSU/DSU

Description: connection to QWEST (BQWNX-DS1NT-10822609)

MTU 1500 bytes, BW 1544 Kbit, DLY 20000 usec,

reliability 252/255, txload 7/255, rxload 2/255

Encapsulation PPP, loopback not set

Keepalive set (10 sec)

LCP Closed, multilink Closed

Closed: CDPCP

Last input 00:01:10, output 00:01:09, output hang never

Last clearing of "show interface" counters 22:09:42

Input queue: 0/75/0/0 (size/max/drops/flushes); Total output drops: 3

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 13000 bits/sec, 0 packets/sec

5 minute output rate 0 bits/sec, 0 packets/sec

1106614 packets input, 476396563 bytes, 0 no buffer

Received 0 broadcasts, 0 runts, 1 giants, 0 throttles

4147 input errors, 1421 CRC, 2535 frame, 0 overrun, 0 ignored, 190 abort

1023144 packets output, 647298686 bytes, 0 underruns

0 output errors, 0 collisions, 13 interface resets

0 output buffer failures, 0 output buffers swapped out

4 carrier transitions

DCD=down DSR=up DTR=up RTS=up CTS=down

What is interesting is that when one is unplugged the plugged in T1 does about 50k of traffic send/receive. I don't know exactly what the traffic is.

I had 3 different people at QWest to check their settings on their router and they say it is correct.

[amit-singh]

Could you please paste the output of the other interface which up and having the traffic of 50 K whhen you unplugged one of the T1. Also when you unplugged the T1 are you able to ping the multilink IP of the ISP side fine or not ?

regards,

-amit singh

[jwhitecomputers]

I cannot ping the other end when one T1 is unplugged.

Here is the interface that is plugged in that still has about 50k of unknown traffic:

Serial0/0 is up, line protocol is up

Hardware is QUICC with integrated T1 CSU/DSU

MTU 1500 bytes, BW 1544 Kbit, DLY 20000 usec,

reliability 255/255, txload 5/255, rxload 2/255

Encapsulation PPP, loopback not set

Keepalive set (10 sec)

LCP Open, multilink Open

Last input 00:00:00, output 00:00:00, output hang never

Last clearing of "show interface" counters 2d00h

Input queue: 0/75/0/0 (size/max/drops/flushes); Total output drops: 1

Queueing strategy: weighted fair [suspended, using FIFO]

FIFO output queue 0/40, 1 drops

5 minute input rate 17000 bits/sec, 12 packets/sec

5 minute output rate 32000 bits/sec, 12 packets/sec

2569469 packets input, 931979593 bytes, 0 no buffer

Received 0 broadcasts, 0 runts, 1 giants, 0 throttles

1773 input errors, 807 CRC, 921 frame, 0 overrun, 0 ignored, 44 abort

2395001 packets output, 1355504590 bytes, 0 underruns

0 output errors, 0 collisions, 2 interface resets

0 output buffer failures, 0 output buffers swapped out

2 carrier transitions

DCD=up DSR=up DTR=up RTS=up CTS=up

*****************************************************

Here is the interface the is unplugged:

Serial1/0 is down, line protocol is down

Hardware is QUICC with integrated T1 CSU/DSU

MTU 1500 bytes, BW 1544 Kbit, DLY 20000 usec,

reliability 252/255, txload 5/255, rxload 2/255

Encapsulation PPP, loopback not set

Keepalive set (10 sec)

LCP Closed, multilink Closed

Closed: CDPCP

Last input 00:00:39, output 00:00:39, output hang never

Last clearing of "show interface" counters 2d00h

Input queue: 0/75/0/0 (size/max/drops/flushes); Total output drops: 8

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 13000 bits/sec, 0 packets/sec

5 minute output rate 0 bits/sec, 0 packets/sec

2540584 packets input, 928388491 bytes, 0 no buffer

Received 0 broadcasts, 0 runts, 10 giants, 0 throttles

120616 input errors, 31133 CRC, 74920 frame, 0 overrun, 0 ignored, 14557 abort

2365831 packets output, 1351544605 bytes, 0 underruns

0 output errors, 0 collisions, 30 interface resets

0 output buffer failures, 0 output buffers swapped out

16 carrier transitions

DCD=down DSR=up DTR=up RTS=up CTS=down

*****************************************************

Here is the multilink interface:

Multilink1 is up, line protocol is up

Hardware is multilink group interface

Internet address is xx.xx.xx.xx/30

MTU 1500 bytes, BW 1544 Kbit, DLY 100000 usec,

reliability 255/255, txload 11/255, rxload 7/255

Encapsulation PPP, loopback not set

Keepalive set (10 sec)

DTR is pulsed for 2 seconds on reset

LCP Open, multilink Open

Open: IPCP

Last input 00:00:23, output never, output hang never

Last clearing of "show interface" counters 2d00h

Input queue: 0/75/0/0 (size/max/drops/flushes); Total output drops: 693

Queueing strategy: fifo

Output queue :0/40 (size/max)

5 minute input rate 47000 bits/sec, 15 packets/sec

5 minute output rate 67000 bits/sec, 15 packets/sec

5071624 packets input, 1829439230 bytes, 0 no buffer

Received 0 broadcasts, 0 runts, 0 giants, 0 throttles

0 input errors, 0 CRC, 0 frame, 0 overrun, 0 ignored, 0 abort

4722447 packets output, 2668968818 bytes, 0 underruns

0 output errors, 0 collisions, 0 interface resets

0 output buffer failures, 0 output buffers swapped out

0 carrier transitions

[amit-singh]

Hi,

That's what I was expecting that when you unplug the T1 you will not be able to ping the other side. If you are able to ping the otherside when you have second T1 connected I guess there is come misconfiguration at your end or ISP end or could be the media problem as I am seeing a lot of input errors on your interface.

It could be that your second media is not through and that's why u r not able to ping the otherside but this point goes void as you have told us that the moment you have both T1's up you see 3 M traffic... now are you sure about this...... I think when you have both the T1's connected tarffic still goes via only 1 link...

Let us know that if you unplug both the T1's one by one do you see the same symptom's at your end.i.e you are unable to route the traffic or does these sympotoms exist only on 1 T1. You should check that.

Now to better troubleshoot it Please try working on local and remote loops from ISP. Unplug your 1 T1 and ask you ISP to ping your multilink IP and I am sure that they will not be able to ping it.. that's when they will start working on this issue with priority...

When you take a local loop from your modem or CSU/DSU make sure that you are able to ping the local IP at your end on both the T1's. Make sure that you donot get any CRC's or input errors.

Now Ask your ISP to give remote loop from their end towards you end and then you try to ping the local IP's at your end and check for the input errors on both the T1's one-by one...... do the vice-versa from your end towards ISP end.

Let me know how it goes....

regards,

-amit singh

[jwhitecomputers]

I know I am getting 3M both ways because I can do a speed test on a remote server we have in a data center and get about 350KB/Sec Upload and Download.

How exactly do I perform this remote loop? Can you give me step by step?

When I unplug one T1 they cannot ping my router and I cannot ping theirs. They say since the configuration is OK I need to call cisco to further resolve this. I do not have a SmartNet contract yet nor do I have phone number.

[don.fortes]

Don't just uplugged the connection. Admin'd it down or remove it from the multi link group.

[jwhitecomputers]

Yeap - tried that too...

It looks like setting "ppp multilink fragmentation-delay 50" makes it work the way it should - I can unplug one or shut it down and it will work of one T1 .

However, they wanted me to disable fragmentation. Does anyone know the drawbacks of either?

[thisisshanky]

Jwhite,

If you configure both T1's with individual ip addreses (dummy addresses will do) and no Multilink, are you able to ping the remote end on each serial interface from the router ?

[st_kannan]

Hi,

Your router will support cef? If yes means enable that one.

Under Global Mode:

Router(config)# ip cef.

Under Physical interface:

Router(config-if)# keepalive

Router(config-if)# no ppp multilink fragmentation.

Enabling fragmentation reduces the delay latency among bundle links, but adds some load to the CPU. Disabling fragmentation may result in better throughput.

If your data traffic is consistently of a similar size, we recommend disabling fragmentation. In this case, the benefits of fragmentation may be outweighed by the added load on the CPU.

Also check the multilink status that is it is bundling both physical interface correctly or not?

Router# show ppp multilink

Also set uniform queuing method under all interfaces.

I hope it will work.

Regards,

KANNAN.S.T.