Why does Facebook spoof the source IP address of the hop before this server?
They spoof the source IP address that is performing the traceroute.
66.220.156.68
maybe their loadbalancer is a little wonky? (I don't see this in
traceroutes from a few places, but I also don't end up at IAD for
'www.facebook.com' traceroutes... here's my last 4 hops though to the
dest-ip you had:
.13.28.75) 0.597 ms ae0.dr08.ash2.tfbnw.net (31.13.26.235) 0.576 ms
8 * * *
9 * * *
10 * * *
11 edge-star-mini-shv-07-ash4.facebook.com (66.220.156.68) 0.774 ms
0.755 ms 0.701 ms
Why does Facebook spoof the source IP address of the hop before this server?
They spoof the source IP address that is performing the traceroute.
...
(31.13.28.207) 67.846 ms ae12.dr08.ash3.tfbnw.net (31.13.29.191) 68.629 ms
12 * * *
13 * * *
14 8.25.38.1 (8.25.38.1) 68.571 ms 68.718 ms 68.132 ms
15 edge-star-mini-shv-07-ash4.facebook.com (66.220.156.68) 67.903 ms 67.752
ms 68.071 ms
---Hop 14 is the source ip of the traceroute which is forged. This essentially
makes hop 14 reply using the same ip for src and dst.
If intentional, I would speculate that this might be something to help their support staff by giving them confirmation of where the traceroute actually originated from in the public Internet view given that the originator might actually be behind possibly several layers of NAT. The two missing hops could be a marker or perhaps other info that got eaten due to various source filters?
maybe their loadbalancer is a little wonky? (I don't see this in
traceroutes from a few places, but I also don't end up at IAD for
'www.facebook.com' traceroutes... here's my last 4 hops though to the
dest-ip you had:.13.28.75) 0.597 ms ae0.dr08.ash2.tfbnw.net (31.13.26.235) 0.576 ms
8 * * *
9 * * *
10 * * *
11 edge-star-mini-shv-07-ash4.facebook.com (66.220.156.68) 0.774 ms
0.755 ms 0.701 ms
This is probably because you are properly filtering your own prefixes from being sourced outside coming in?
unclear, that traceroute was from someplace I don't own the network for...
from another place I do though...
5 ae0.dr07.ash2.tfbnw.net (31.13.26.233) 4 ms
ae0.dr05.ash3.tfbnw.net (31.13.29.21) 4 ms ae0.dr08.ash2.tfbnw.net
(31.13.26.235) 2 ms
6 * * *
7 * * *
8 * * *
9 edge-star-mini-shv-07-ash4.facebook.com (66.220.156.68) 3 ms 3 ms 2 ms
same-ish results, no spoofed bits.
Why does Facebook spoof the source IP address
of the hop before this server? They spoof the
source IP address that is performing the traceroute.
It's a known bug; apologies. I've asked again that we rollout the fix.
https://atlas.ripe.net/measurements/3612424/#!probes
I did a atlas measurement of 500 probes, 104 probes (21%) had their
outside IP shown in traceroute. Some peers of AS32934 don't have
ingress filtering. It seems all prefixes advertised by Facebook are
ROA signed and valid tho.