From: Shahid Shafi (sshafi@gmail.com)
Date: Mon Jul 19 2004 - 07:43:14 GMT-3
---------- Forwarded message ----------
From: Shahid Shafi <sshafi@gmail.com>
Date: Sun, 18 Jul 2004 01:39:20 -0700
Subject: Re: 3550 COnnectivity (and re: ENCAP FAILURES ON ETHERNET)
To: Brian McGahan <bmcgahan@internetworkexpert.com>
Interesting discussion. It actually brings up one interesting question
in my mind. Will a router respond or proxy arp for ANY address if it
has a default route and offcourse with proxy arp enabled on that
interface. I thought proxy arping is done by router for only directly
connected interfaces on the router.
Any input is greatly appreciated.
Thx
Shahid
On Sun, 18 Jul 2004 03:59:49 -0400, Brian McGahan
<bmcgahan@internetworkexpert.com> wrote:
> Alex,
>
> Yes it does, as does the router when ip routing is disabled.
> I'm not sure why they implemented it this way, but they did. See the
> below output:
>
> R3--R1--SW1
>
> R3#sh ip int brief | exclude unassigned
> Interface IP-Address OK? Method Status
> Protocol
> Serial1/2 13.0.0.3 YES manual up up
>
> R3#show ip route
> <snip>
> Gateway of last resort is 0.0.0.0 to network 0.0.0.0
>
> C 13.0.0.0/8 is directly connected, Serial1/2
> S* 0.0.0.0/0 is directly connected, Serial1/2
>
> R1#show ip int brief | exclude unassigned
> Interface IP-Address OK? Method Status
> Protocol
> Ethernet0/0 10.0.0.1 YES manual up up
>
> Serial0/1 13.0.0.1 YES manual up up
>
> R1#show int e0/0 | include bia
> Hardware is AmdP2, address is 0004.c057.32c0 (bia 0004.c057.32c0)
>
> SW1#show ip route
> Default gateway is not set
>
> Host Gateway Last Use Total Uses Interface
> ICMP redirect cache is empty
> SW1#show ip int brief | ex unassigned
> Interface IP-Address OK? Method Status
> Protocol
> Vlan1 10.0.0.7 YES manual up up
>
> SW1#ping 13.0.0.3
>
> Type escape sequence to abort.
> Sending 5, 100-byte ICMP Echos to 13.0.0.3, timeout is 2 seconds:
> !!!!!
> Success rate is 100 percent (5/5), round-trip min/avg/max = 28/229/1028
> ms
> SW1#
> IP ARP: creating incomplete entry for IP address: 13.0.0.3 interface
> Vlan1
> IP ARP: sent req src 10.0.0.7 000a.b7dc.a880,
> dst 13.0.0.3 0000.0000.0000 Vlan1
> IP ARP: rcvd rep src 13.0.0.3 0004.c057.32c0, dst 10.0.0.7 Vlan1
>
> Although it is not connected nor does it have a default gateway,
> SW1 ARPs for 13.0.0.3. The ARP is answered by R1 by proxy, as R1 has a
> route to the destination 13.0.0.3.
>
> When IP routing is enabled SW1 is limited to ARPing to routes
> that are installed in the routing table:
>
> SW1#conf t
> Enter configuration commands, one per line. End with CNTL/Z.
> SW1(config)#ip routing
> SW1(config)#end
> SW1#debug ip packet
> IP packet debugging is on
> SW1#debug arp
> ARP packet debugging is on
> SW1#ping 13.0.0.3
>
> Type escape sequence to abort.
> Sending 5, 100-byte ICMP Echos to 13.0.0.3, timeout is 2 seconds:
>
> datagramsize=100, IP 59: s=10.0.0.7 (local), d=13.0.0.3, totlen 100,
> fragment 0, fo 0, unroutable.
> datagramsize=100, IP 60: s=10.0.0.7 (local), d=13.0.0.3, totlen 100,
> fragment 0, fo 0, unroutable.
> datagramsize=100, IP 61: s=10.0.0.7 (local), d=13.0.0.3, totlen 100,
> fragment 0, fo 0, unroutable.
> datagramsize=100, IP 62: s=10.0.0.7 (local), d=13.0.0.3, totlen 100,
> fragment 0, fo 0, unroutable.
> datagramsize=100, IP 63: s=10.0.0.7 (local), d=13.0.0.3, totlen 100,
> fragment 0, fo 0, unroutable.
> Success rate is 0 percent (0/5)
>
> As you can see from the above output the ARP process is not
> initiated because there is no route to the destination.
>
> This actually fits in with the other thread I just responded to
> re: ENCAP FAILURES ON ETHERNET. The ARP process occurs after routing.
> When routing is not enabled ARP will always occur.
>
> HTH,
>
> Brian McGahan, CCIE #8593
> bmcgahan@internetworkexpert.com
>
> Internetwork Expert, Inc.
> http://www.InternetworkExpert.com
> Toll Free: 877-224-8987 x 705
> Outside US: 775-826-4344 x 705
> 24/7 Support: http://forum.internetworkexpert.com
> Live Chat: http://www.internetworkexpert.com/chat/
>
> > -----Original Message-----
> > From: Alexander Arsenyev (GU/ETL)
> [mailto:alexander.arsenyev@ericsson.com]
> > Sent: Sunday, July 18, 2004 2:38 AM
> > To: Brian McGahan; ccielab@groupstudy.com
> > Subject: RE: 3550 COnnectivity
> >
> > So will Cat3550 with one VLAN interface with IP address, say
> 10.0.0.1/16,
> > ip routing disabled, ip default-gateway not configured, ARP for an IP
> > address 11.0.0.1? I'm pretty much sure it won't do ARP with "ip
> routing"
> > statement in config.
> > Don't have a Cat3550 to test it now :-)
> > Cheers
> > Alex
> >
> > -----Original Message-----
> > From: Brian McGahan [mailto:bmcgahan@internetworkexpert.com]
> > Sent: 18 July 2004 08:31
> > To: Alexander Arsenyev (GU/ETL); ccielab@groupstudy.com
> > Subject: RE: 3550 COnnectivity
> >
> >
> > When bridging IP it will ARP for everything (same with the
> > routers if you turn ip routing off). If you're routing IP you'll only
> > ARP for destinations that you have a route to. If by changing the
> mask
> > on a connected interface you encompass the destination in the
> connected
> > network it will ARP for it. Assuming the device on the other end
> > supports proxy-arp transmission will be successful. It's a fun
> exercise
> > in routing logic.
> >
> > Brian McGahan, CCIE #8593
> > bmcgahan@internetworkexpert.com
> >
> > Internetwork Expert, Inc.
> > http://www.InternetworkExpert.com
> > Toll Free: 877-224-8987 x 705
> > Outside US: 775-826-4344 x 705
> > 24/7 Support: http://forum.internetworkexpert.com
> > Live Chat: http://www.internetworkexpert.com/chat/
> >
> >
> > > -----Original Message-----
> > > From: nobody@groupstudy.com [mailto:nobody@groupstudy.com] On Behalf
> > Of
> > > Alexander Arsenyev (GU/ETL)
> > > Sent: Sunday, July 18, 2004 2:20 AM
> > > To: ccielab@groupstudy.com
> > > Subject: RE: 3550 COnnectivity
> > >
> > > I believe that Cat3550 will ARP for "everything" IF IP
> address/netmask
> > > combination
> > > on VLAN interface covers that "everything". That's why sometimes
> it's
> > > important
> > > to trick Cat3550 into thinking that "everything" is directly
> > connected,
> > > see
> > > my earlier post
> > > http://www.groupstudy.com/archives/ccielab/200406/msg01843.html
> > >
> > > HTH,
> > > Cheers
> > > Alex
> > >
> > > -----Original Message-----
> > > From: nobody@groupstudy.com [mailto:nobody@groupstudy.com]On Behalf
> Of
> > > Brian McGahan
> > > Sent: 18 July 2004 01:29
> > > To: Kenneth Wygand; Mike Calhoon; Lord, Chris;
> ccielab@groupstudy.com
> > > Subject: RE: 3550 COnnectivity
> > >
> > >
> > > Ken,
> > >
> > > Your statements are true to a degree. Technically the 3550 is
> > > not using proxy-arp. Instead, it is just ARPing for everything. It
> > is
> > > the router that responds on behalf of the destination that is being
> > > ARPed for (hence proxy-arp).
> > >
> > > I only mention this point because it is the router on the
> > > attached segment that must be running proxy-arp, and not the switch
> > > itself.
> > >
> > >
> > > HTH,
> > >
> > > Brian McGahan, CCIE #8593
> > > bmcgahan@internetworkexpert.com
> > >
> > > Internetwork Expert, Inc.
> > > http://www.InternetworkExpert.com
> > > Toll Free: 877-224-8987 x 705
> > > Outside US: 775-826-4344 x 705
> > > 24/7 Support: http://forum.internetworkexpert.com
> > > Live Chat: http://www.internetworkexpert.com/chat/
> > >
> > >
> > > > -----Original Message-----
> > > > From: nobody@groupstudy.com [mailto:nobody@groupstudy.com] On
> Behalf
> > > Of
> > > > Kenneth Wygand
> > > > Sent: Saturday, July 17, 2004 5:23 PM
> > > > To: Mike Calhoon; Lord, Chris; ccielab@groupstudy.com
> > > > Subject: RE: 3550 COnnectivity
> > > >
> > > > Mike,
> > > >
> > > > Without specifying the "ip default-gateway", your 3550 will
> default
> > to
> > > > using proxy-arp to resolve your IP addresses to MAC addresses. If
> > > your
> > > > attached router (on the VLAN where your switch's IP address is)
> > > supports
> > > > proxy-arp, it will resolve and your ping will succeed.
> > > >
> > > > You should have entries if you do a "show arp" when using
> proxy-arp,
> > > but I
> > > > don't believe those entries will exist when crossing VLANs if you
> > have
> > > a
> > > > default gateway configured (just your default gateway will be in
> > your
> > > > local arp table).
> > > >
> > > > If you can, try it out both ways and post your outputs! :)
> > > >
> > > > Hope this helps,
> > > > Ken
> > > >
> > > > ________________________________
> > > >
> > > > From: nobody@groupstudy.com on behalf of Mike Calhoon
> > > > Sent: Sat 7/17/2004 6:18 PM
> > > > To: 'Lord, Chris'; ccielab@groupstudy.com
> > > > Subject: RE: 3550 COnnectivity
> > > >
> > > >
> > > >
> > > > Chris,
> > > >
> > > > I have wondered the same thing lately. I have found that as long
> > as
> > > the
> > > > rest of my routers have the route to the VLAN installed, I can
> ping
> > > the ip
> > > > on the switch without having to add "ip default-gateway", ip
> > routing,
> > > or
> > > > anything else to it. So full connectivity is being reached, but I
> > am
> > > > wondering if I should be adding "ip default-gateway" or anything
> > extra
> > > to
> > > > the switch.
> > > >
> > > >
> > > > Thanks,
> > > > Mike
> > > >
> > > >
> > > > -----Original Message-----
> > > > From: nobody@groupstudy.com [mailto:nobody@groupstudy.com] On
> Behalf
> > > Of
> > > > Lord, Chris
> > > > Sent: Saturday, July 17, 2004 5:03 PM
> > > > To: ccielab@groupstudy.com
> > > > Subject: 3550 COnnectivity
> > > >
> > > > Please could I ask for some opinions.......
> > > >
> > > > A lot of practice lab scenarios state standard assumptions such as
> > "do
> > > not
> > > > use static or default routes on any router, etc" and "full
> > > connectivity
> > > > must
> > > > be attained, etc". Suppose we met this in the real lab, my
> question
> > is
> > > > this... if one of the switches has a vlan interface with an ip
> > address
> > > > assigned to it then I assume the pod should be able to ping it and
> > > > vica-versa. If the switch is not running an IGP, is the use of "ip
> > > > default-gateway" permissible or does this break the rules?
> > > >
> > > > If you can't use "ip default-gateway" do you think configuring
> irdp
> > on
> > > the
> > > > attached router in the switch's management vlan would be a good
> > > > alternative?
> > > >
> > > > thx in anticipation,
> > > >
> > > > Chris.
> > > >
> > > >
> > > >
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