HDLC serial up/up (looped)
Posted on 2003-12-11
I'm setting up a HDLC 256k connection.
Router on both ends are Cisco 1601.
If I enable keepalives on the serial interface it shows that it is looped. Output from "debug serial int" shows:
00:28:59: Serial0: HDLC myseq 121, mineseen 120*, yourseen 121, line up (looped)
00:29:09: Serial0: HDLC myseq 122, mineseen 121*, yourseen 122, line up (looped)
00:29:19: Serial0: HDLC myseq 123, mineseen 122*, yourseen 123, line up (looped)
#sho int ser 0
Serial0 is up, line protocol is up (looped)
Hardware is QUICC Serial
Description: connected to C.DATALINK
Internet address is 22.214.171.124/24
MTU 1500 bytes, BW 1544 Kbit, DLY 20000 usec, rely 255/255, load 1/255
Encapsulation HDLC, loopback not set, keepalive set (10 sec)
Last input 00:00:08, output 00:00:08, output hang never
Last clearing of "show interface" counters 00:08:57
Input queue: 0/75/0 (size/max/drops); 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)
5 minute input rate 0 bits/sec, 0 packets/sec
5 minute output rate 0 bits/sec, 0 packets/sec
131 packets input, 10049 bytes, 0 no buffer
Received 62 broadcasts, 0 runts, 0 giants, 0 throttles
0 input errors, 0 CRC, 0 frame, 0 overrun, 0 ignored, 0 abort
131 packets output, 10049 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
I would think this to be a mis-configuration of the telco equipment. Someone else called them and they supposedly tested it and it was OK. What think you ?
The exact same behaviour happens on both routers when keepalives are set on the serial interface. Without keepalives, it doesn't complain about being looped (yes I know, how can it detect a loop if keepalives are not being used). I can ping the IP address of the local serial interface, but not the remote one.
The other thing that makes me think the local CSU/DSU is in loopback mode is the fact that the number of packets input & output are the same. Is this a correct assumption ? I need facts to go and acuse the telco with, but I haven't done much work with HDLC (or other point-to-point) lines.
Config of router looks like this (very plain):
service timestamps debug uptime
service timestamps log uptime
enable password **
no ip domain-lookup
description connected to EthernetLAN
ip address 126.96.36.199 255.255.255.0
no ip directed-broadcast
description connected to C.DATALINK
ip address 188.8.131.52 255.255.255.0
no ip directed-broadcast
ip route 184.108.40.206 255.255.255.0 220.127.116.11
ip route 18.104.22.168 255.255.255.0 22.214.171.124 permanent
ip route 126.96.36.199 255.255.255.0 188.8.131.52 permanent
ip route 184.108.40.206 255.255.255.0 220.127.116.11 permanent
line con 0
exec-timeout 0 0
transport input none
line vty 0 4
The other router is identical config (with IP addresses changed, obviously).
I don't think this is a difficult question (I could be wrong), but it is urgent, hence the 500 points.
I'm going home now and will be back in 12 hours. Hopefully there will be an answer waiting for me when I get back...