From: Scott Morris (swm@emanon.com)
Date: Mon Jun 20 2005 - 21:17:10 GMT-3
Likely not... But a google search never hurts either. :)
TTL exceeded has to do with that TTL hop count thing we all love.
Time-exceeded has to do with time to reassemble fragmented packets.
http://www.networksorcery.com/enp/protocol/icmp/msg11.htm
You do also need to ponder where to draw the line between useful and inane.
While the lab does come up with some really oddball stuff to test your
knowledge of a protocol's operation, everything is searchable on the DocCD
someplace!
Scott
-----Original Message-----
From: nobody@groupstudy.com [mailto:nobody@groupstudy.com] On Behalf Of
ccie2be
Sent: Monday, June 20, 2005 6:25 PM
To: 'Brian Dennis'; 'Group Study'
Subject: RE: icmp - time-exceeded vs ttl-exceeded
Hi Brian,
As you suggested I did look through the archives and found some interesting
things that refreshed my memory about reflexive acl's and Traceroute in
general.
But, none of the posts I could find talked about the difference between
time-exceeded vs ttl-exceeded.
I accept the fact that I need to permit time-exceeded to fulfill the tasks
in IE lab 2 and 3, but I'm still curious as to the difference between these
2 icmp options.
My hope is that if I really knew the difference, it would be easier to
remember which one to use under the pressure of the lab.
Thanks, Tim
-----Original Message-----
From: nobody@groupstudy.com [mailto:nobody@groupstudy.com] On Behalf Of
Brian Dennis
Sent: Monday, June 20, 2005 5:31 PM
To: ccie2be; Group Study
Subject: RE: icmp - time-exceede vs ttl-exceeded
Tim,
You should search the archive as there was a long discussion on this
topic about a year ago. Also as far as using the traceroute option for the
ICMP type, if you understand how traceroute works you'll know why you don't
use it.
Brian Dennis, CCIE #2210 (R&S/ISP-Dial/Security)
bdennis@internetworkexpert.com
Internetwork Expert, Inc.
http://www.InternetworkExpert.com
Toll Free: 877-224-8987
Direct: 775-745-6404 (Outside the US and Canada)
-----Original Message-----
From: nobody@groupstudy.com [mailto:nobody@groupstudy.com] On Behalf Of
ccie2be
Sent: Monday, June 20, 2005 2:02 PM
To: Group Study
Subject: icmp - time-exceede vs ttl-exceeded
Hi guys,
Let's assume I want to configure a reflexive acl which allows Traceroute
packets back in.
I'm trying to make sure I select the correct icmp type packet to allow
back-in. But, when I do the following I see lots of options.
R5(config)#access-list 101 perm icmp any any ?
<0-255> ICMP message type
administratively-prohibited Administratively prohibited
alternate-address Alternate address
conversion-error Datagram conversion
dod-host-prohibited Host prohibited
dod-net-prohibited Net prohibited
dscp Match packets with given dscp value
echo Echo (ping)
echo-reply Echo reply
fragments Check non-initial fragments
general-parameter-problem Parameter problem
host-isolated Host isolated
host-precedence-unreachable Host unreachable for precedence
host-redirect Host redirect
host-tos-redirect Host redirect for TOS
host-tos-unreachable Host unreachable for TOS
host-unknown Host unknown
host-unreachable Host unreachable
information-reply Information replies
information-request Information requests
log Log matches against this entry
log-input Log matches against this entry, including
input
interface
mask-reply Mask replies
mask-request Mask requests
mobile-redirect Mobile host redirect
net-redirect Network redirect
net-tos-redirect Net redirect for TOS
net-tos-unreachable Network unreachable for TOS
net-unreachable Net unreachable
network-unknown Network unknown
no-room-for-option Parameter required but no room
option-missing Parameter required but not present
packet-too-big Fragmentation needed and DF set
parameter-problem All parameter problems
port-unreachable Port unreachable
precedence Match packets with given precedence value
precedence-unreachable Precedence cutoff
protocol-unreachable Protocol unreachable
reassembly-timeout Reassembly timeout
redirect All redirects
router-advertisement Router discovery advertisements
router-solicitation Router discovery solicitations
source-quench Source quenches
source-route-failed Source route failed
time-exceeded All time exceededs <-----
**************
time-range Specify a time-range
timestamp-reply Timestamp replies
timestamp-request Timestamp requests
tos Match packets with given TOS value
traceroute Traceroute
<-----------#############
ttl-exceeded TTL exceeded
<-------------*****************
unreachable All unreachables
<cr>
Notice how similar the 2 "starred" options look. What's the difference
between these 2 options?
Also, if I need to allow Traceroute back-in, why wouldn't I use the
traceroute option?
TIA, Tim
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