[j-nsp] port mirror to multiple ports on MX80 in inet6

[Clarke Morledge]

Paul,

In your last example, assuming that your cisco router is hanging off your 
mirror source port, ge-1/0/2, it makes sense from my experience that your 
"x.x.158.13 > x.x.158.194: ICMP echo reply" shows up in your mirror 
output, as I mentioned earlier, but not the ICMP echo request in the other 
direction.  The echo request enters your L2 configured port, but since it 
then crosses a subnet boundary by hitting your irb.100, the MX will not 
treat it as L2 any more for mirroring purposes.

So if you do a Layer3 port mirror with irb.100 as your mirror source, you 
should be able to see the packet.

Traffic coming out of the IRB egressing out the L2 mirror source port gets 
treated as L2, which is why the L2 mirror works in that direction.  There 
is something about the way Integrated Routing and Bridging works that 
accounts for this, but I do not fully understand it.

With respect to the vlan tag/un-tag, because you changed the vlan-id to 
1000 in the bridge-domain, as the original packet had a vlan tag of 100, 
this changes the mirrored packet.  It shows up on the mirror output as 
untagged because your "encapsulation ethernet-bridge" on the interface 
will not tag the packet.

I use the "encapsulation flexible-ethernet-services" with 
"flexible-vlan-tagging" and I am able to change the vlan-id of the 
mirrored output if I need to do that.

The other cases you describe have me scratching my head as to what is up, 
but I've seen other weird things with layer2 mirroring that do not make 
much sense to me.  So as to why the behavior between x.x.158.13 and 
x.x.158.5 is reversed now is really puzzling, particularly since traffic 
in both directions should just be L2.

It bugs me that the L2 port mirror examples in the web documentation are 
really poor.  They have made some improvements recently, but Juniper 
really needs to step up and cover these different scenarios in detail. 
Typically, I need to set up a port mirror on the fly for a quick look, but 
unfortunately, I end up messing with JTAC for several weeks trying to get 
something to work that takes about 5 minutes on a Cisco platform.

The flexibility of the Junos platform allows for some complex mirroring, 
which is great, but I have wasted a lot of time trying to get a handle on 
this port mirroring thing and still do not get it..... where I can afford 
it, I just say "Forget it, I'll stick with a tap".

If you can make any better heads or tails out of this, I'd like to hear 
about it.

Clarke Morledge
College of William and Mary
Information Technology - Network Engineering
Jones Hall (Room 18)
Williamsburg VA 23187

On Tue, 23 Oct 2012, Paul Vlaar wrote:

> On 23/10/12 10:59 PM, Clarke Morledge wrote:
>> ---------------------------------------------------
>> My question for you would be if you have an IRB interface associated
>> with the bridge-domain that your mirror source port is in, and if the
>> ICMP traffic coming into the router is hitting that IRB.  If that is the
>> case, the MX will not treat the traffic coming into your IRB interface
>> via your "encapsulation ethernet-bridge" as Layer2 traffic in this
>> context, so it will not get mirrored.
>> -----------------------------------------------------
>
> There is indeed an IRB associated with the bridge-domain of the port to
> be mirrored:
>
> mx80> show configuration bridge-domains VLAN100 routing-interface
> routing-interface irb.100;
>
>> show configuration interfaces irb.100
> family inet {
>    address x.x.158.1/26;
> }
>
> A traceroute from another router that is one L3 hop away from the MX80,
> to the IP address of the host connected to the interface that we're
> doing the port mirror on:
>
> cisco#traceroute x.x.158.13
> Type escape sequence to abort.
> Tracing the route to 199.115.158.13
> VRF info: (vrf in name/id, vrf out name/id)
>  1 x.x.158.193 0 msec 0 msec 0 msec
>  2 x.x.158.13 0 msec 0 msec 0 msec
> cisco#
>
> x.x.158.193 is the address of the point to point link at the MX80, and
> x.x.158.13 is the IP address of the mirrored host.
>
> So as far as I can see it's not hitting the irb.100 address, however it
> is doing this on the return, as it's the default gateway out of the host
> at x.x.158.13. But the return is where we catch the ICMP reply, so that
> part works.
>
> To be complete here, this is the L3 interface where the traffic comes in
> from the other router:
>
> mx80> show configuration interfaces ge-1/3/11
> unit 0 {
>    family inet {
>        address x.x.158.193/30;
>    }
> }
>
> And this is the FIB entry for the target host:
>
> mx80> show route forwarding-table destination x.x.158.13
> Routing table: default.inet
> Internet:
> Destination        Type RtRef Next hop           Type Index NhRef Netif
> x.x.158.13/32  dest     1 0:1b:21:84:d7:a6   ucst   768     4 ge-1/0/2.0
>
> Routing table: default-switch.inet
> Internet:
> Destination        Type RtRef Next hop           Type Index NhRef Netif
> default            perm     0                    rjct   538     1
>
> Routing table: __master.anon__.inet
> Internet:
> Destination        Type RtRef Next hop           Type Index NhRef Netif
> default            perm     0                    rjct   529     1
>
>
>> ------------------------------------------------------
>>
>> With respect to the vlan tagging on the port mirror output interface,
>> the L2 packet being mirrored will egress with the original vlan tag
>> intact, no matter what vlan id you configure on the mirror destination
>> interface.
>>
>> However, if you insert the "vlan-id" keyword into the "bridge-domain"
>> configuration, you can manipulate the vlan tag that gets egressed out of
>> your mirror destination port.  But if the "vlan-id" in the bridge domain
>> is the same as the vlan-id of the mirror destination port, the original
>> packet vlan-id gets preserved on output.
>
> I've tried setting vlan-id on the bridge-domain for the analyzer port:
>
> [edit bridge-domains analyzers]
> mx80# show
> domain-type bridge;
> vlan-id 1000;
> interface ge-1/3/2.0;
>
> After I commit, when I ping from the host connected to the same bridge
> domain as the mirrored port, where before I could see the ICMP request
> go in as well, I now only see the reply:
>
> 17:22:26.067209 00:1b:21:84:d7:a6 > 00:1b:21:86:a5:22, ethertype IPv4
> (0x0800), length 98: x.x.158.13 > x.x.158.5: ICMP echo reply, id 56599,
> seq 2, length 64
> 17:22:27.067850 00:1b:21:84:d7:a6 > 00:1b:21:86:a5:22, ethertype IPv4
> (0x0800), length 98: x.x.158.13 > x.x.158.5: ICMP echo reply, id 56599,
> seq 3, length 64
>
> And what's more it is untagged now.
>
> The same for pinging from the cisco router:
>
> 17:25:22.720228 00:1b:21:84:d7:a6 > 80:71:1f:c6:34:f0, ethertype IPv4
> (0x0800), length 114: x.x.158.13 > x.x.158.194: ICMP echo reply, id 33,
> seq 2, length 80
>
> (previously this was tagged as well)
>
> So perhaps a trick can be found here to make this work both ways...
>
>> I have not tested this, but my guess is that this might also apply to
>> packets being mirrored that are untagged at the source.
>>
>> Port mirroring on this platform is enough to make your head spin.
>
> I unfortunately have to agree on that.
>
> 	~paul
>
>