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PPP ACK / NACK Timing Out

I have a T3 connection between two Cisco 3725s. Looking at the PPP longs I see a repetition of this pattern:

*Mar 1 04:23:01.712 pst: Se1/0 LCP: I CONFREQ [ACKsent] id 239 len 14

*Mar 1 04:23:01.712 pst: Se1/0 LCP: MRU 4470 (0x01041176)

*Mar 1 04:23:01.712 pst: Se1/0 LCP: MagicNumber 0x31EA3BB3 (0x050631EA3BB3)

*Mar 1 04:23:01.712 pst: Se1/0 LCP: O CONFACK [ACKsent] id 239 len 14

*Mar 1 04:23:01.712 pst: Se1/0 LCP: MRU 4470 (0x01041176)

*Mar 1 04:23:01.712 pst: Se1/0 LCP: MagicNumber 0x31EA3BB3 (0x050631EA3BB3)

*Mar 1 04:23:02.168 pst: Se1/0 LCP: TIMEout: State ACKsent

*Mar 1 04:23:02.168 pst: Se1/0 LCP: O CONFREQ [ACKsent] id 100 len 14

*Mar 1 04:23:02.168 pst: Se1/0 LCP: MRU 4470 (0x01041176)

*Mar 1 04:23:02.168 pst: Se1/0 LCP: MagicNumber 0x0F2DC891 (0x05060F2DC891)

*Mar 1 04:23:03.728 pst: Se1/0 PPP: I pkt type 0xC021, datagramsize 18 link[ppp

]

It seems that this router can receive packets just fine, but the othe router is not seeing my ACKs. I do not have access to the other router unfortunantly. What would cause one direction of communication to crap out?

Here is the relevant part of my config file:

interface Serial1/0

mtu 4470

bandwidth 40000

ip address 10.1.1.2 255.255.255.252

encapsulation ppp

no ip route-cache

no ip mroute-cache

delay 20

autodetect encapsulation ppp

dsu mode 3

dsu bandwidth 44210

scramble

serial restart_delay 0

5 REPLIES
Hall of Fame Super Silver

Re: PPP ACK / NACK Timing Out

Shawn

Can you verify that both ends are configured with scramble? In fact can you verify that all the dsu parameters match between the routers? I know that your post says that you do not have access to the other router but can you get someone there to give you their configuration parameters?

From your description that it looks like you receive from the other end but that they do not receive from you it sounds like some kind of mismatch. And I would start with the dsu parameters.

Of course there is also some possibility that yout receive side is good but your transmit side has some physical fault. You might ask the provider to do some testing of the circuit.

HTH

Rick

New Member

Re: PPP ACK / NACK Timing Out

Thanks for the info Rick.

I have some configuration info for the other router and the DSU between the two routers. The DSU is indeed set to scramble on the interface that we use, however the other router uses an HSSI interface that isn't set to scramble.

I'm going to play around with the settings a bit. Do the MTU, bandwidth, etc have to be identical on both sides?

Hall of Fame Super Silver

Re: PPP ACK / NACK Timing Out

Shawn

If one side is set for scramble and the other is not I suspect that this is an issue.

I believe that MTU does not cause a problem if it does not match on both sides. Regular bandwidth does not matter if it does not match on both sides (but if dsu bandwidth is configured you should be careful - in most cases I think it must match).

HTH

Rick

New Member

Re: PPP ACK / NACK Timing Out

I come back this morning and I'm no longer getting incoming packets... what else can go wrong?

New Member

Re: PPP ACK / NACK Timing Out

Even when I'm turning on local loopback, I'm still getting line protocol down.

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