UDP ports used for traceroute

July 7, 2006 @ 9:07 am · Filed under CCIE Study

Thanks for the great information on traceroute!
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From: nobody@groupstudy.com on behalf of Brian Dennis Sent: Wed 7/5/2006 2:03 PM To: elias.chari@gmail.com; ccielab@groupstudy.com Subject: RE: UDP ports used for traceroute

Note that traceroute is a technique to have the routers between the source and destination reveal themselves and finally have the destination reveal itself by replying to a “packet”. Traceroute can be implemented using ICMP, UDP, and even TCP so as an “Internetwork Expert” when someone asks you to filter “traceroute” you should get a little background as to the traceroute application/OS’s being used to trigger the reply from the destination. Example: Windows uses ICMP echoes by default, most Linux OS’s use UDP by default but can use ICMP echoes (-I option), and the IOS uses UDP.
The goal of traceroute is to have the routers between the source and destination reveal themselves and finally have the destination reply so that you know you have reached it. The routers reveal themselves by sending Time Exceeded (aka TTL-Exceeded) ICMP packets back to the source when the TTL is decremented to zero. The traceroute implementation can know its reached the destination by having it reply to an ICMP echo request, send an ICMP port unreachable to a packet sent to an unused UDP port, or completing the TCP three way handshake.
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ICMP based traceroute:
In this example we are sending ICMP echo requests to www.cisco.com and looking for the ICMP echo reply to know that we have reached the destination.
[root@CoachZ root]# traceroute -I www.cisco.com traceroute to www.cisco.com (198.133.219.25), 30 hops max, 38 byte packets 1 198.132.102.1 (198.132.102.1) 1.658 ms 1.975 ms 1.968 ms 2 foo.hostrack.net (202.101.143.254) 5.394 ms 22.382 ms 2.966 ms 3 ser4-0.core01.las.switchcommgroup.com (66.209.64.41) 20.132 ms 20.494 ms 20.195 ms 4 pos1-0.core02.las.oc48a.switchcommgroup.com (66.209.64.218) 19.749 ms 25.827 ms 26.814 ms 5 500.POS4-0.GW1.VEG2.alter.net (157.130.238.193) 29.108 ms 19.864 ms 20.066 ms 6 129.at-0-0-0.CL1.PHX2.ALTER.NET (152.63.115.26) 26.338 ms 26.232 ms 26.821 ms 7 0.so-4-0-0.XL1.SJC2.ALTER.NET (152.63.55.101) 46.424 ms 45.996 ms 45.675 ms 8 POS1-0.XR1.SJC2.ALTER.NET (152.63.56.138) 48.653 ms 46.513 ms 46.803 ms 9 193.ATM7-0.GW5.SJC2.ALTER.NET (152.63.48.77) 46.693 ms 46.619 ms 46.446 ms 10 ciscosys-gw1.customer.alter.net (65.208.80.242) 46.556 ms 46.954 ms 46.944 ms 11 sjce-dmzbb-gw1.cisco.com (128.107.239.89) 30.818 ms 31.769 ms 32.685 ms 12 sjck-dmzdc-gw1.cisco.com (128.107.224.69) 30.589 ms 30.626 ms 30.448 ms 13 * * * 14 www.cisco.com (198.133.219.25) 28.916 ms 28.994 ms 28.944 ms
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UDP based traceroute:
In this example we are sending UDP packets with a starting port number of 33434 to www.cisco.com. Note that we don’t ever get a reply from www.cisco.com because their firewall will not allow our UDP packets in.
[root@CoachZ root]# man traceroute | grep “UDP port number” -p Set the base UDP port number used in probes (default is 33434). [root@CoachZ root]# [root@CoachZ root]# traceroute www.cisco.com traceroute to www.cisco.com (198.133.219.25), 30 hops max, 38 byte packets 1 198.132.102.1 (198.132.102.1) 1.725 ms 1.866 ms 1.841 ms 2 foo.hostrack.net (202.101.143.254) 4.887 ms 4.281 ms 4.482 ms 3 ser4-0.core01.las.switchcommgroup.com (66.209.64.41) 21.266 ms 21.152 ms 20.826 ms 4 pos1-0.core02.las.oc48a.switchcommgroup.com (66.209.64.218) 58.829 ms 42.033 ms 24.007 ms 5 500.POS4-0.GW1.VEG2.alter.net (157.130.238.193) 21.448 ms 23.277 ms 21.446 ms 6 129.at-0-0-0.CL1.PHX2.ALTER.NET (152.63.115.26) 27.816 ms 27.259 ms 27.210 ms 7 0.so-4-0-0.XL1.SJC2.ALTER.NET (152.63.55.101) 47.540 ms 46.954 ms 47.198 ms 8 POS1-0.XR1.SJC2.ALTER.NET (152.63.56.138) 48.072 ms 47.247 ms 46.667 ms 9 193.ATM7-0.GW5.SJC2.ALTER.NET (152.63.48.77) 51.728 ms 51.437 ms 48.304 ms 10 ciscosys-gw1.customer.alter.net (65.208.80.242) 48.563 ms 48.878 ms 47.807 ms 11 sjce-dmzbb-gw1.cisco.com (128.107.239.89) 31.562 ms 32.653 ms 31.318 ms 12 sjck-dmzdc-gw1.cisco.com (128.107.224.69) 32.327 ms 31.831 ms 31.516 ms 13 * * * 14 * * *
************************************************************************ ************************** TCP based traceroute:
In this example we are sending TCP SYN packets to port 80 looking for the destination to complete the three-way-handshake. Once the handshake is complete we know that we have reached the destination. Obviously Cisco’s firewall is going to allow packets to TCP port 80 into its web server.
[root@CoachZ root]# tcptraceroute www.cisco.com tcptraceroute: Symbol `pcap_version’ has different size in shared object, consider re-linking Selected device eth3, address 198.132.102.93, port 41440 for outgoing packets Tracing the path to www.cisco.com (198.133.219.25) on TCP port 80, 30 hops max 1 198.132.102.1 (198.132.102.1) 1.575 ms 1.507 ms 1.469 ms 2 foo.hostrack.net (202.101.143.254) 4.840 ms 5.090 ms 4.596 ms 3 ser4-0.core01.las.switchcommgroup.com (66.209.64.41) 21.205 ms 20.895 ms 21.430 ms 4 pos1-0.core02.las.oc48a.switchcommgroup.com (66.209.64.218) 21.682 ms 21.012 ms 21.059 ms 5 500.POS4-0.GW1.VEG2.alter.net (157.130.238.193) 21.185 ms 21.304 ms 20.939 ms 6 129.at-0-0-0.CL1.PHX2.ALTER.NET (152.63.115.26) 27.176 ms 28.615 ms 27.644 ms 7 0.so-4-0-0.XL1.SJC2.ALTER.NET (152.63.55.101) 47.659 ms 48.220 ms 47.667 ms 8 POS1-0.XR1.SJC2.ALTER.NET (152.63.56.138) 47.534 ms 48.483 ms 47.183 ms 9 193.ATM7-0.GW5.SJC2.ALTER.NET (152.63.48.77) 64.413 ms 51.058 ms 49.007 ms 10 ciscosys-gw1.customer.alter.net (65.208.80.242) 48.156 ms 49.197 ms 47.534 ms 11 sjce-dmzbb-gw1.cisco.com (128.107.239.89) 31.685 ms 32.633 ms 32.895 ms 12 sjck-dmzdc-gw1.cisco.com (128.107.224.69) 32.291 ms 33.900 ms 35.461 ms 13 www.cisco.com (198.133.219.25) [open] 31.041 ms 31.667 ms 32.775 ms [root@CoachZ root]#
HTH, 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 elias.chari@gmail.com Sent: Wednesday, July 05, 2006 6:46 AM To: ccielab@groupstudy.com Subject: UDP ports used for traceroute
Hi Guys,
Does anybody know them?
I think they are 30000 and above but not sure…
Also if you want to match them in an access-list how do you do it since the only option is gt, i.e
Rack1R1(config)#ip access-list extended UDP Rack1R1(config-ext-nacl)#perm udp any any ? dscp Match packets with given dscp value eq Match only packets on a given port number fragments Check non-initial fragments gt Match only packets with a greater port number log Log matches against this entry log-input Log matches against this entry, including input interface lt Match only packets with a lower port number neq Match only packets not on a given port number option Match packets with given IP Options value precedence Match packets with given precedence value range Match only packets in the range of port numbers reflect Create reflexive access list entry time-range Specify a time-range tos Match packets with given TOS value
would you do gt 29999 ?
Thanks Elias