From: Stefan Grey (examplebrain@hotmail.com)
Date: Tue Aug 16 2005 - 05:47:39 GMT-3
Hello,
In this lab routers R2 and R3 are connected by to wires and between them is
connected the multilink ppp over frame relay so:
R6- r2- (ppp multilink) - r3 - sw2
Between all routers is configured ospf. Look what happens when we try to
ping R6 from sw2:
Pay attention: the datagramsize of the ping packets is changed from 100 to
114 thats why only 1st packet is successfull. (Why?!! and why the packet
size is changed)
Look further after this output:
CAT2#debug ip packet
IP packet debugging is on
CAT2#ping 174.1.26.6
Type escape sequence to abort.
Sending 5, 100-byte ICMP Echos to 174.1.26.6, timeout is 2 seconds:
08:50:07: datagramsize=100, IP 28: s=174.1.38.8 (local), d=174.1.26.6,
totlen 100, fragment 0, fo 0, cef process switched
08:50:07: datagramsize=100, IP 28: s=174.1.38.8 (local), d=174.1.26.6
(FastEthernet0/1), totlen 100, fragment 0, fo 0, sending
08:50:07: datagramsize=114, IP 28: s=174.1.38.8 (local), d=174.1.26.6
(FastEthernet0/1), totlen 100, fragment 0, fo 0, sending full packet.
08:50:09: datagramsize=98, IP 7717: s=174.1.38.3 (FastEthernet0/1),
d=224.0.0.5, totlen 80, fragment 0, fo 0, rcvd 0
08:50:09: datagramsize=100, IP 29: s=174.1.38.8 (local), d=174.1.26.6,
totlen 100, fragment 0, fo 0, cef process switched
08:50:09: datagramsize=100, IP 29: s=174.1.38.8 (local), d=174.1.26.6
(FastEthernet0/1), totlen 100, fragment 0, fo 0, sending
08:50:09: datagramsize=114, IP 29: s=174.1.38.8 (local), d=174.1.26.6
(FastEthernet0/1), totlen 100, fragment 0, fo 0, sending full packet
(FastEthernet0/1), totlen 68, fragment 0, fo 0, sending full packet.
08:50:11: datagramsize=100, IP 30: s=174.1.38.8 (local), d=174.1.26.6,
totlen 100, fragment 0, fo 0, cef process switched
08:50:11: datagramsize=100, IP 30: s=174.1.38.8 (local), d=174.1.26.6
(FastEthernet0/1), totlen 100, fragment 0, fo 0, sending
08:50:11: datagramsize=114, IP 30: s=174.1.38.8 (local), d=174.1.26.6
(FastEthernet0/1), totlen 100, fragment 0, fo 0, sending full packet.
08:50:13: datagramsize=100, IP 31: s=174.1.38.8 (local), d=174.1.26.6,
totlen 100, fragment 0, fo 0, cef process switched
08:50:13: datagramsize=100, IP 31: s=174.1.38.8 (local), d=174.1.26.6
(FastEthernet0/1), totlen 100, fragment 0, fo 0, sending
08:50:13: datagramsize=114, IP 31: s=174.1.38.8 (local), d=174.1.26.6
(FastEthernet0/1), totlen 100, fragment 0, fo 0, sending full packet.
08:50:15: datagramsize=100, IP 32: s=174.1.38.8 (local), d=174.1.26.6,
totlen 100, fragment 0, fo 0, cef process switched
08:50:15: datagramsize=100, IP 32: s=174.1.38.8 (local), d=174.1.26.6
(FastEthernet0/1), totlen 100, fragment 0, fo 0, sending
08:50:15: datagramsize=114, IP 32: s=174.1.38.8 (local), d=174.1.26.6
(FastEthernet0/1), totlen 100, fragment 0, fo 0, sending full packet.
Success rate is 0 percent (0/5)
CAT2#un all
All possible debugging has been turned off
CAT2#
CAT2#ping 174.1.26.6
Type escape sequence to abort.
Sending 5, 100-byte ICMP Echos to 174.1.26.6, timeout is 2 seconds:
!....
Success rate is 20 percent (1/5), round-trip min/avg/max = 56/56/56 ms
CAT2#
When we make the ping with the lower packet size everything is just ok:
CAT2#ping
Protocol [ip]:
Target IP address: 174.1.26.6
Repeat count [5]:
Datagram size [100]: 20
% A decimal number between 36 and 18024.
Datagram size [100]: 36
Timeout in seconds [2]:
Extended commands [n]:
Sweep range of sizes [n]:
Type escape sequence to abort.
Sending 5, 36-byte ICMP Echos to 174.1.26.6, timeout is 2 seconds:
!!!!!
Please explain this strange behaviour. Thanks
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