RTT of ICMP "TTL exceeded" messages in Level3 network remains the same throughout the network
Hugo Slabbert
hslabbert at stargate.ca
Wed Aug 13 15:41:24 UTC 2014
>How does this technically work? What are the advantages of such setup?
http://forums.juniper.net/t5/Routing/what-does-quot-icmp-tunneling-quot-mean-in-mpls-vpn/td-p/164284
http://www.juniper.net/techpubs/en_US/junos12.1/topics/usage-guidelines/mpls-configuring-icmp-message-tunneling.html
...and from
https://www.nanog.org/meetings/nanog49/presentations/Sunday/mpls-nanog49.pdf:
> Some networks also run MPLS-only cores, which carry no IP routes.
> • This presents a problem, since if they did want to show the hops in
> traceroute, the router can’t do IP routing to return the ICMP TTL
> Exceed.
> • To solve this problem, an “icmp tunneling” feature was implemented.
> • If an ICMP message is generated inside an LSP, the ICMP message is
> carried all the way to the end of the LSP before being routed back.
> • This can make traceroute look really weird, since you see all the hops
> along the LSP, but they all appear to have the same latency as the final
> hop. This causes much end-user confusion.
--
Hugo
On Wed 2014-Aug-13 18:25:11 +0300, Martin T <m4rtntns at gmail.com> wrote:
>Hi,
>
>if I make a traceroute to a host in San Jose in Level3 network from
>DigitalOcean server in Amsterdam, then in Level3 network(hop 6 in
>example below) the RTT remains the same:
>
># traceroute -q 1 -I ZYNGA-INC.edge1.SanJose3.Level3.net
>traceroute to ZYNGA-INC.edge1.SanJose3.Level3.net (4.53.208.114), 30
>hops max, 60 byte packets
> 1 5.101.103.253 (5.101.103.253) 0.265 ms
> 2 95.85.0.229 (95.85.0.229) 0.236 ms
> 3 ix-4-2-0-0.tcore1.AV2-Amsterdam.as6453.net (195.219.194.25) 0.275 ms
> 4 if-7-2.tcore1.AD1-Amsterdam.as6453.net (195.219.194.46) 0.630 ms
> 5 4.68.63.41 (4.68.63.41) 0.635 ms
> 6 vl-3603-ve-227.csw2.Amsterdam1.Level3.net (4.69.162.153) 155.309 ms
> 7 ae-56-221.ebr2.Amsterdam1.Level3.net (4.69.153.201) 155.627 ms
> 8 ae-46-46.ebr2.London1.Level3.net (4.69.143.74) 153.470 ms
> 9 *
>10 ae-61-61.csw1.NewYork1.Level3.net (4.69.134.66) 148.972 ms
>11 *
>12 ae-2-2.ebr1.SanJose1.Level3.net (4.69.135.185) 147.881 ms
>13 ae-91-91.csw4.SanJose1.Level3.net (4.69.153.14) 149.632 ms
>14 ae-4-90.edge1.SanJose3.Level3.net (4.69.152.208) 151.107 ms
>15 ZYNGA-INC.edge1.SanJose3.Level3.net (4.53.208.114) 154.431 ms
>#
>
>In other words, one sees the RTT of the end-host as a RTT for all the
>hops in Level3 netwotk. If I make the traceroute to penultimate hop
>ae-4-90.edge1.SanJose3.Level3.net, then RTT is as expected:
>
>root at vserver:~# traceroute -q 1 -I ae-4-90.edge1.SanJose3.Level3.net
>traceroute to ae-4-90.edge1.SanJose3.Level3.net (4.69.152.208), 30
>hops max, 60 byte packets
> 1 5.101.103.254 (5.101.103.254) 0.228 ms
> 2 95.85.0.237 (95.85.0.237) 0.217 ms
> 3 ix-4-2-0-0.tcore1.AV2-Amsterdam.as6453.net (195.219.194.25) 0.276 ms
> 4 if-7-2.tcore1.AD1-Amsterdam.as6453.net (195.219.194.46) 0.656 ms
> 5 4.68.63.41 (4.68.63.41) 0.607 ms
> 6 vl-3604-ve-228.csw2.Amsterdam1.Level3.net (4.69.162.157) 0.696 ms
> 7 ae-56-221.ebr2.Amsterdam1.Level3.net (4.69.153.201) 0.677 ms
> 8 ae-45-45.ebr2.London1.Level3.net (4.69.143.70) 7.059 ms
> 9 ae-44-44.ebr1.NewYork1.Level3.net (4.69.137.78) 76.311 ms
>10 ae-81-81.csw3.NewYork1.Level3.net (4.69.134.74) 76.265 ms
>11 ae-82-82.ebr2.NewYork1.Level3.net (4.69.148.41) 76.820 ms
>12 ae-2-2.ebr1.SanJose1.Level3.net (4.69.135.185) 149.101 ms
>13 ae-91-91.csw4.SanJose1.Level3.net (4.69.153.14) 150.557 ms
>14 ae-4-90.edge1.SanJose3.Level3.net (4.69.152.208) 162.022 ms
>root at vserver:~#
>
>All the ICMP "TTL exceeded" messages except the first and the
>penultimate one in Level3 network have MPLS extensions
>header(s24.postimg.org/4z9at9z45/ICMP_echo_reply_MPLS_extensions.png)
>which is always the same except the tag value changes.
>
>How does this technically work? What are the advantages of such setup?
>
>
>thanks,
>Martin
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