From: Joel Amao (femmy79@hotmail.com)
Date: Tue Oct 09 2007 - 19:30:22 ART
John,
turn off proxy arp on SW2 and find out for yourself. :)
Joel Amao
CCIE#18128
> Date: Tue, 9 Oct 2007 21:38:28 +0200> From: johmoor@gmail.com> To:
gsherr@gmail.com; ggombas@gmail.com; ccielab@groupstudy.com> Subject: Re:
Interesting behaviour of the switch svi> > to guys: No everything is
configured just as simple as I described. No> errors in the configuration. IP
proxy arp is not explicitly configured but> probably yes it is enabled by
default.> Let's look again into the topology> >
sw1-vlan30-------vlan30-sw2-vlan50------------------vlan50--sw3> > Between
sw1,sw2 and sw3 is just a simple dot1q trunk.> Configuration:> sw1-vlan30:
30.30.30.2> sw2-vlan50: 30.30.30.1> sw2-vlan50: 50.50.50.1> sw3-vlan50:
50.50.50.2> On all trunks configuration is really very simple:> switchport>
switchport trunk enc dot1q> sw mode trunk> > on vlans like:> vlan 30> ip
address 30.30.30.2> switch 2.> vlan 30> ip address 30.30.30.1> vlan 50> ip
address 50.50.50.1> ...> > sw1 vlan 30 int can bing vlan 3 vlan 50 int withou
any default gateway or> routing configured. Proxy arp.. yes maybe.> But
question is still the same:> sw3 can receive proxy arp reply from sw2 but how
can it forward packet> without having any routing entry in its table? The PC
can actually send a> packet out it's interface without default gateway
configured if it receives> proxy arp reply. Maybe it is the same with the
switch?> > Any thoughts?> > P.S http://www.tildefrugal.net/tech/arp.php look
here what PC do if it don't> have default-gateway configured...> > > On
10/9/07, John Moor <johmoor@gmail.com> wrote:> >> > to guys: No everything is
configured just as simple as I described. No> > errors in the configuration.
IP proxy arp is not explicitly configured but> > probably yes it is enabled by
default.> > Let's look again into the topology> >> >
sw1-vlan30-------vlan30-sw2-vlan50------------------vlan50--sw3> >> > Between
sw1,sw2 and sw3 is just a simple dot1q trunk.> > Configuration:> > sw1-vlan30:
30.30.30.2> > sw2-vlan50: 30.30.30.1> > sw2-vlan50: 50.50.50.1> > sw3-vlan50:
50.50.50.2> > On all trunks configuration is really very simple:> >
switchport> > switchport trunk enc dot1q> > sw mode trunk> >> > on vlans
like:> > vlan 30> > ip address 30.30.30.2> > switch 2.> > vlan 30> > ip
address 30.30.30.1> > vlan 50> > ip address 50.50.50.1> > ...> >> > sw1 vlan
30 int can bing vlan 3 vlan 50 int withou any default gateway or> > routing
configured. Proxy arp.. yes maybe.> > But question is still the same:> > sw3
can receive proxy arp reply from sw2 but how can it forward packet> > without
having any routing entry in its table? The PC can actually send a> > packet
out it's interface without default gateway configured if it receives> > proxy
arp reply. Maybe it is the same with the switch?> >> > Any thoughts?> >> > P.S
http://www.tildefrugal.net/tech/arp.php look here what PC do if it> > don't
have default-gateway configured...> >> > On 10/9/07, Guy Sherr
<gsherr@gmail.com> wrote:> > >> > > Think about this. The only way for sw2 to
be able to forward between> > > 30.30.30.2> > > and 50.50.50.2 is if sw2 is
under the impression that they are on the> > > same vlan> > > (unless you have
an IP route in sw2; I am assuming this at L2 and not> > > L3).> > >> > > Dot1q
does not tag the native vlan unless you tell it to. If you have> > > native
untagged> > > and make the sw2->sw1 trunk native vlan 50, then (obviously)
traffic> > > without a tag> > > is "understood to be on vlan 50." However, if
sw1 has vlan 30> > > configured native, then> > > it will be "understanding"
those untagged frames on the trunk to be on> > > vlan 30.> > >> > > Are you
getting a vlan mismatch maybe?> > >> > > On 10/8/07, John Moor
<johmoor@gmail.com > wrote:> > > >> > > > Hello, guys!> > > > I have mentioned
interesting behaviour. Could you pleas confirm this> > > > or tell> > > > that
this is incorrect?> > > >
sw1-vlan30-------vlan30-sw2-vlan50------------------vlan50--sw3> > > >> > > >
Between sw1,sw2 and sw3 is just a simple dot1q trunk.> > > > Configuration:> >
> > sw1-vlan30: 30.30.30.2> > > > sw2-vlan50: 30.30.30.1> > > > sw2-vlan50:
50.50.50.1> > > > sw3-vlan50: 50.50.50.2> > > >> > > > I can ping from
50.50.50.2 to 30.30.30.2 even without configuring> > > > default-gateway on sw
3. I assume that it happenes because when sw3> > > > doesn't> > > > know the
route it just broadcasts the ip packet and the same does sw1> > > > in> > > >
opposite to the router.> > > >> > > > Is it correct? Or there is some other
explanation of this. Thank you.> > > >> > > >
This archive was generated by hypermail 2.1.4 : Fri Nov 16 2007 - 13:11:13 ART