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X25 configuration , verification and debugging

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X25 is definitely old and legacy, but still there are people out there who use it and there are ISP out there who support it, when I started looking for more docs on X25 I could not find much, so I decided to create one myself.

TOPOLOGY

router-2800-2 --Serial1/0----------------------------------Serial2/0--X25-switch-2900-4--s0/1/0:1-----------------------------------------s0/3/0:1---router-2800-3

CONFIGURATION

2800-2#sh run int s1/0

interface Serial1/0

ip address 10.1.1.1 255.255.255.0

encapsulation x25

x25 address 1234

x25 map ip 10.1.1.2 5678 broadcast

dsu bandwidth 44210

end

2800-3#sh run int s0/3/0:1

interface Serial0/3/0:1

ip address 10.1.1.2 255.255.255.0

encapsulation x25

x25 address 5678

x25 map ip 10.1.1.1 1234 broadcast

end

2900-4#conf t

2900-4#x25 routing

2900-4#x25 route 1234 interface Serial2/0

2900-4#x25 route 5678 interface Serial0/1/0:1

2900-4#sh run int s2/0

interface Serial2/0

no ip address

encapsulation x25 dce

dsu bandwidth 44210

end

2900-4#sh run int s0/1/0:1

interface Serial0/1/0:1

no ip address

encapsulation x25 dce

VERIFICATION

2900-4#sh x25 route

# Match                         Substitute         Route to     match/use

1 dest 1234                                         Serial2/0               0/0

2 dest 5678                                         Serial01/0:1         1/1

2800-2#sh x25 vc

SVC 1024, State: D1, Interface: Serial1/0

Started 00:10:07, last input 00:10:02, output 00:10:02

Connects 5678 <-> ip 10.1.1.2

Call PID cisco, Data PID none

Window size input: 2, output: 2

Packet size input: 128, output: 128

PS: 6 PR: 6 ACK: 5 Remote PR: 6 RCNT: 1 RNR: no

P/D state timeouts: 0 timer (secs): 0

data bytes 3000/3000 packets 30/30 Resets 0/0 RNRs 0/0 REJs 0/0 INTs 0/0

2800-2#ping 10.1.1.2

Type escape sequence to abort.

Sending 5, 100-byte ICMP Echos to 10.1.1.2, timeout is 2 seconds:

!!!!!

Success rate is 100 percent (5/5), round-trip min/avg/max = 4/4/8 ms

2800-2#sh int s1/0

Serial1/0 is up, line protocol is up

Hardware is DSXPNM Serial

Internet address is 10.1.1.1/24

MTU 4470 bytes, BW 44210 Kbit/sec, DLY 200 usec,

     reliability 255/255, txload 1/255, rxload 1/255

Encapsulation X25, crc 16, loopback not set

Keepalive set (10 sec)

X.25 DTE, version 1984, address 1234, state R1, modulo 8, timer 0

     Defaults: idle VC timeout 0

       cisco encapsulation

     RESTARTs 0/0 CALLs 1+3/0+0/0+0 DIAGs 0/0

LAPB DTE, state CONNECT, modulo 8, k 7, N1 35816, N2 20

2800-2#sh x25 map

Serial1/0: X.121 5678 <-> ip 10.1.1.2

permanent, broadcast, 1 VC: 1024

“debug x25 packet” on 2900-2 while ping 10.1.1.2 from 2800-2 , packets being sent out (O) and received in (I)

2900-4#debug x25I

X.25 packet debugging is on

2900-4#

*May 27 02:17:02.946: Serial2/0: X.25 I D1 Data (103) 8 lci 1024 PS 3 PR 3

*May 27 02:17:02.946: Serial0/1/0:1: X.25 O D1 Data (103) 8 lci 1 PS 3 PR 3

*May 27 02:17:02.950: Serial0/1/0:1: X.25 I D1 Data (103) 8 lci 1 PS 3 PR 4

*May 27 02:17:02.950: Serial2/0: X.25 O D1 Data (103) 8 lci 1024 PS 3 PR 4

*May 27 02:17:02.950: Serial2/0: X.25 I D1 Data (103) 8 lci 1024 PS 4 PR 4

*May 27 02:17:02.950: Serial0/1/0:1: X.25 O D1 Data (103) 8 lci 1 PS 4 PR 4

*May 27 02:17:02.954: Serial0/1/0:1: X.25 I D1 Data (103) 8 lci 1 PS 4 PR 5

*May 27 02:17:02.954: Serial2/0: X.25 O D1 Data (103) 8 lci 1024 PS 4 PR 5

*May 27 02:17:02.954: Serial2/0: X.25 I D1 Data (103) 8 lci 1024 PS 5 PR 5

*May 27 02:17:02.954: Serial0/1/0:1: X.25 O D1 Data (103) 8 lci 1 PS 5 PR 5

*May 27 02:17:02.958: Serial0/1/0:1: X.25 I D1 Data (103) 8 lci 1 PS 5 PR 6

*May 27 02:17:02.958: Serial2/0: X.25 O D1 Data (103) 8 lci 1024 PS 5 PR 6

*May 27 02:17:02.958: Serial2/0: X.25 I D1 Data (103) 8 lci 1024 PS 6 PR 6

*May 27 02:17:02.958: Serial0/1/0:1: X.25 O D1 Data (103) 8 lci 1 PS 6 PR 6

*May 27 02:17:02.962: Serial0/1/0:1: X.25 I D1 Data (103) 8 lci 1 PS 6 PR 7

*May 27 02:17:02.962: Serial2/0: X.25 O D1 Data (103) 8 lci 1024 PS 6 PR 7

*May 27 02:17:02.962: Serial2/0: X.25 I D1 Data (103) 8 lci 1024 PS 7 PR 7

*May 27 02:17:02.962: Serial0/1/0:1: X.25 O D1 Data (103) 8 lci 1 PS 7 PR 7

*May 27 02:17:02.966: Serial0/1/0:1: X.25 I D1 Data (103) 8 lci 1 PS 7 PR 0

*May 27 02:17:02.966: Serial2/0: X.25 O D1 Data (103) 8 lci 1024 PS 7 PR 0

“debug x25 events” on 2900-2 while shut and no shut on int s1/0 on 2800-2 , look for cause code.

2900-4#

*May 27 02:19:42.314: Serial2/0: X.25 O R/Inactive Restart (5) 8 lci 0

*May 27 02:19:42.314:  Cause 7, Diag 0 (Network operational/No additional information)

*May 27 02:19:42.314: Serial2/0: X.25 I R3 Restart (5) 8 lci 0

*May 27 02:19:42.314:   Cause 0, Diag 0 (DTE originated/No additional information)

X25 over tcp coming soon ....... keep checking.....


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