Hairpin NAT on CC disabled - EC2 inconsistency

[Kiall Mac Innes]

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Impact statement: This bug causes several issues warranting a fix in maverick/lucid

A) Prevents correct communication between instances (eg icmp-reply from priv IP when pub IP was ping'd)
B) Blocks communication to the local instance via its public ip
C) Breaks compatibility with EC2

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On EC2, This ping succeeds as would be expected:

# ping `curl --quite http://169.254.169.254/2008-02-01/meta-data/public-ipv4`

On UEC, The same ping command fails. Additionally on UEC, an instance pinging another instances public IP receives echo-reply's from the second instances private IP, rather than the public IP ping'd.

The offending firewall rule (as seen by "iptables -L -t nat -n") is:
MASQUERADE all -- 172.19.0.0/16 !172.19.0.0/16

When changed to:
MASQUERADE all -- 172.19.0.0/16 0.0.0.0/0

Ping's work as expected (both pings to your "local" public IP, and other instances public IPs)

The bug appears to be in net/vnetwork.c L200:

snprintf(cmd, 256, "-A POSTROUTING -d ! %s/%d -s %s/%d -j MASQUERADE", network, slashnet, network, slashnet);

should be changed to:

snprintf(cmd, 256, "-A POSTROUTING -s %s/%d -j MASQUERADE", network, slashnet);

Hope this makes sense ;) Its been a *long* 2 days.

[graziano obertelli (graziano.obertelli)]

I believe this issues is fixed in 2.0.3.