[mrtg-developers] Re: MRTG over IPv6 tested with experimental Cisco IOS

[Rafael Martinez Torres]

On Tue, 20 May 2003, Lorenzo Colitti wrote:

>
> This is because the SNMP agent is replying using a different IPv6
> address than the one the query was sent to. This is what tcpdump shows:
>
> > # tcpdump -nv -s1514 ip6 and port 161
> > tcpdump: listening on eth0
> > 13:47:37.168819 2001:760:4:0:204:76ff:fe22:5ba0.34475 > 2001:618:10:2a03:205:1cff:fe00:1df0.161: [udp sum ok]  { SNMPv1 { GetNextRequest(26) R=-1263143579  .1.3.6.1.2.1.1} }  (len 49, hlim 64)
> > 13:47:37.650208 2001:800:40:2a03:205:1cff:fe00:1df0.161 > 2001:760:4:0:204:76ff:fe22:5ba0.34475: [udp sum ok]  { SNMPv1 { GetResponse(108) R=-1263143579  .1.3.6.1.2.1.1.1.0="Linux lisa.consulintel.euro6ix.org 2.4.18-3 #1 Thu Apr 18 07:31:07 EDT 2002 i586"} }  (len 131, hlim 54)
>

Good ! Very accurate !.

Some fuzzy ideas, don't trust them dogmatically:

You are tracking ip6 traffic with source-origin on port 161 on your
machine.

The parameters above "ip6 and port 161" do not constraint  the type for
transmission protocol , I mean [tcp/udp]/ipv6 .

If your patch is asking with tcp/ip6, both ip6 addresses must match , and
this would justify the problem

 But...what when udp/ipv6 is used ?

Can you configure the SNMPd agent running on my PC to reply from the same
address always ? Or can you constraint just to listen on a fixed IPv6
address ?

If not, (please, confirm), the patch would present a problem

I do use for running SNMPD ( net-snmp )

"#./snmpd -V -f -a -d -L udp6:161"


> cfgmaker is sending requests to 2001:618:10:2a03:205:1cff:fe00:1df0, but
> snmpd is replying from 2001:800:40:2a03:205:1cff:fe00:1df0. So cfgmaker
> doesn't see the reply.
>
> But if I use the other address, it works fine:
>
> > $ ./cfgmaker --enable-ipv6 public@[2001:800:40:2a03:205:1cff:fe00:1df0]:161 -o /dev/null
> > --base: IPv6 libraries found, IPv6 enabled.
> > --base: Get Device Info on public@[2001:800:40:2a03:205:1cff:fe00:1df0]:161
> > --base: Vendor Id:
> > --base: Populating confcache
> > --snpo: confcache public@[2001:800:40:2a03:205:1cff:fe00:1df0]:161 Descr lo --> 1
> > --snpo: confcache public@[2001:800:40:2a03:205:1cff:fe00:1df0]:161 Descr sit0 --> 2
> > [...]
>
>

Sorry , even changing to the other address I have the same result: I
cannot
to confirm your solution . :-|

Valerio's patch:
>>>>>>>>>>>>>>>>>>>>>>>>>>>>>>>>>>>>>>>>>>>>>>>>>>>>>>>>>>>>>>>>>>>>>>>>>>>>>>>>>>>>>>>>>>>>>
$cfgmaker --enable-ipv6 public@[2001:800:40:2a03:205:1cff:fe00:1df0]:161
--base: IPv6 libraries found, IPv6 enabled.
--base: Get Device Info on public@[2001:800:40:2a03:205:1cff:fe00:1df0]:161
SNMP Error:
send_query:
SNMPv1_Session (remote host: "2001:800:40:2a03:205:1cff:fe00:1df0" [2001:800:40:2a03:205:1cff:fe00:1df0].161)
                  community: "public"
                 request ID: 1299910885
                PDU bufsize: 8000 bytes
                    timeout: 2s
                    retries: 5
                    backoff: 1)
 at /home/itl/bin/../lib/mrtg2/SNMP_util.pm line 590
SNMPWALK Problem for 1.3.6.1.2.1.1 on public@[2001:800:40:2a03:205:1cff:fe00:1df0]:161
 at /home/itl/bin/cfgmaker line 766
--base: No response using IPv6 for public@[2001:800:40:2a03:205:1cff:fe00:1df0]:161, trying again using IPv4
SNMP Error:
close: Bad file descriptor
>>>>>>>>>>>>>>>>>>>>>>>>>>>>>>>>>>>>>>>>>>>>>>>>>>>>>>>>>>>>>>>>>>>>>>>>>>>>>>>>>>>>>>>>>>>>>>>


On my patch I got succesfull on both addresses :
Rafael's patch (note thereis no "--enable-ipv6" flag, automatically
detects the family class:
>>>>>>>>>>>>>>>>>>>>>>>>>>>>>>>>>>>>>>>>>>>>>>>>>>>>>>>>>>>>>>>>>>>>>>>>>>>>>>>>>>>>>>>>
$cfgmaker  public@[2001:800:40:2a03:205:1cff:fe00:1df0]:161
--base: Get Device Info on public@[2001:800:40:2a03:205:1cff:fe00:1df0]:
--base: Vendor Id:
--base: Populating confcache
--snpo: confcache public@[2001:800:40:2a03:205:1cff:fe00:1df0]: Descr lo --> 1
--snpo: confcache public@[2001:800:40:2a03:205:1cff:fe00:1df0]: Descr sit0 --> 2
--snpo: confcache public@[2001:800:40:2a03:205:1cff:fe00:1df0]: Descr eth0 --> 3
--snpo: confcache public@[2001:800:40:2a03:205:1cff:fe00:1df0]: Descr eth1 --> 4
>>>>>>>>>>>>>>>>>>>>>>>>>>>>>>>>>>>>>>>>>>>>>>>>>>>>>>>>>>>>>>>>>>>>>>>>>>>>>>>>>>>>

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