[Pkg-exim4-users] Problems concerning IPv6 Port 25's opening to the Internet

Satoru Otsubo trnsnt at otip.jp
Mon Oct 29 16:48:25 UTC 2012

Thank you,

> On Sun, Oct 28, 2012 at 03:54:38AM +0900, Satoru Otsubo wrote:
> >  Why is Port 25 shown as "filtered" ?
> Many ISPs filter tcp/25 to protect the internet from their users' open
> relays. Use tcpdump to check whether your connections from outside
> come through.

(1) With the command "tcpdump -vv dst host eeee:....:ffff and port 25",
      (eeee:....:ffff is my PC's ipv6 address)
I was able to see ipv6 packets coming from bendel.debian.org.
  (bendel.debian.org is debian-user at lists.debian.org, which I subscribe.)
Therefore, it seems that my PC's ipv6 port 25 is open.

(2) Next, I investigated bendel.debian.org's IPv6 port 25 with the probing PC:
  (My PC and the probing PC are connected to the same ISP. )
# host bendel.debian.org
    bendel.debian.org has address
    bendel.debian.org has IPv6 address 2001:41b8:202:deb:216:36ff:fe40:4002
# nmap -6 -p 25 2001:41b8:202:deb:216:36ff:fe40:4002
This resulted in "filtered", although debian-user at lists.debian.org accepts mailings from its users.

>From (1) and (2), can I say that the ISP blocks the packets with dst port 25 coming from its users ?

> By the way, what does HGW mean?

HGW is Home Gate Way, which does RA(Router advertisements), simple packet filtering, etc.


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