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RE: ICMP redirects posted 11/12/2003
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I can't think of a configurable option, but consider this.

1. configure up a route-map that matches on packet length and drops the
packet if it's too big

route-map my_map deny 5
match length 1548 1550

int xxx x/x
ip policy my_map etc etc

you need to check out the values here - may be in bits, I don't know

2. the router would presumably send back a icmp unreachable - but without
the MTU info you specify below.

3. good luck


-----Original Message-----
From: nobody@xxxxxxxxxxxxxx [mailto:nobody@xxxxxxxxxxxxxx]On Behalf Of
Sent: 12 November 2003 15:54
To: ccielab@xxxxxxxxxxxxxx
Subject: OT: ICMP redirects

Hello all,

RFC 1191 specifies that ICMP unreachable packets for MTU issues must contain
the MTU of the next hop.

Is there any way to make Cisco behaviour non-RFC compliant, I mean, to send
the ICMP unreachable packets WITHOUT the next hop MTU in the payload?

In other words, I would like to suppress the "01 cc" extra information from
the ICMP payload in the following packet:

================================ IP Header (inbound -- [ICS])
Source: Dest:
       len:  56      ttl: 255   proto: 1      cksum:  0x330c      id: 0x365
     flags:  NONE    tos: 0x0  hdrlen: 20    offset:  0x0     optlen: 0
-------------------------------- ICMP Header
type: UNREACH            chksum: 0x5ee1
code: IP_DF caused drop
~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~ IP Header/Data
   0: 45 00 05 dc 99 0e 40 00 3f 06 18 bb c0 a8 02 01  E.....@x?.......
  16: c0 a8 01 01 cc fd 00 14 d4 63 fa b0 -- -- -- --  .........c......

Please note I am NOT asking how to suppress ICMP redirects nor how to use
adjust-mss, path-mtu-discovery, etc... I already tested those options and
understood how they work.

I guess the answer is: Cisco is RFC compliant, no way to suppress this info
from the ICMP PDU, but I wanted to ask just in case.

Best regards,

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