L3 interface on 4948
in [Cisco]
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From: unix on 27 Apr 2010 09:52 I configured "no switchport" with IP address on my 4948 and all is well when I have something plugged into that interface. (I can ping the interface address from nodes attached to the VLANs on the switch and whatever is attached to the L3 interface). BUT, when I unplug nodes directly connected to the L3 port, I can't ping the L3 port IP for some reason. Is there something I need to do so that it remains up even if there are no physical connections to the L3 port?
From: berkid on 27 Apr 2010 10:55 berkid had written this in response to http://www.telecom-gear.com/cisco/L3-interface-on-4948-61123-.htm : unix wrote: -- Its not possible for phisycal interface to remain up even if its unpluged. I don't understand why do you need that exactly, but maybe a loopback interface can solve your problem or using a loopback interface and the ip unnumbered loopback 0 command on the L3 interface. ##-----------------------------------------------## Telecom Discussions at http://www.telecom-gear.com/ no-spam access to your favorite newsgroup - comp.dcom.sys.cisco - 51948 messages and counting! ##-----------------------------------------------##
From: bod43 on 27 Apr 2010 12:00 On 27 Apr, 15:55, berkdan_at_freemail_dot...(a)foo.com (berkid) wrote: > berkid had written this in response tohttp://www.telecom-gear.com/cisco/L3-interface-on-4948-61123-.htm : > > unix wrote: > Its not possible for phisycal interface to remain up even if its unpluged.. > I don't understand why do you need that exactly, but maybe a loopback > interface can solve your problem or using a loopback interface and the ip > unnumbered loopback 0 command on the L3 interface. It is I think possible to have a physical interface up even if nothing is connected. int x no keepalive Hmmm. I just tried on an 877. Did not work on the switch ports. They are unusual though. Not usually something you would ever want to do though. For example RIP could advertise unreachable networks.
From: unix on 28 Apr 2010 00:27 On Apr 27, 11:00 am, bod43 <Bo...(a)hotmail.co.uk> wrote: > On 27 Apr, 15:55, berkdan_at_freemail_dot...(a)foo.com (berkid) wrote: > > > berkid had written this in response tohttp://www.telecom-gear.com/cisco/L3-interface-on-4948-61123-.htm : > > > unix wrote: > > Its not possible for phisycal interface to remain up even if its unpluged. > > I don't understand why do you need that exactly, but maybe a loopback > > interface can solve your problem or using a loopback interface and the ip > > unnumbered loopback 0 command on the L3 interface. > > It is I think possible to have a physical interface up > even if nothing is connected. > > int x > no keepalive > > Hmmm. I just tried on an 877. Did not work on the > switch ports. They are unusual though. > > Not usually something you would ever want to do though. > For example RIP could advertise unreachable networks. Let me clarify. Let's say my L3 port is assigned 10.10.10.11 and I have a PC directly connected to that interface with ip 10.10.10.12. From a VLAN on that switch, I can ping 10.10.10.11 and 10.10.10.12. When I unplug the PC, I can't ping the L3 interface address any more. There has to be a way to keep it up since it's just a virtual ip similar to VLAN ip address that we define when we want to enable VLAN routing. Makes sense?
From: bod43 on 28 Apr 2010 05:14 On 28 Apr, 05:27, unix <unix...(a)yahoo.com> wrote: > On Apr 27, 11:00 am, bod43 <Bo...(a)hotmail.co.uk> wrote: > > > > > On 27 Apr, 15:55, berkdan_at_freemail_dot...(a)foo.com (berkid) wrote: > > > > berkid had written this in response tohttp://www.telecom-gear.com/cisco/L3-interface-on-4948-61123-.htm : > > > > unix wrote: > > > Its not possible for phisycal interface to remain up even if its unpluged. > > > I don't understand why do you need that exactly, but maybe a loopback > > > interface can solve your problem or using a loopback interface and the ip > > > unnumbered loopback 0 command on the L3 interface. > > > It is I think possible to have a physical interface up > > even if nothing is connected. > > > int x > > no keepalive > > > Hmmm. I just tried on an 877. Did not work on the > > switch ports. They are unusual though. > > > Not usually something you would ever want to do though. > > For example RIP could advertise unreachable networks. > > Let me clarify. Let's say my L3 port is assigned 10.10.10.11 and I > have a PC directly connected to that interface with ip > 10.10.10.12. From a VLAN on that switch, I can ping 10.10.10.11 and > 10.10.10.12. When I unplug the PC, I can't ping the L3 interface > address any more. There has to be a way to keep it up since it's just > a virtual ip similar to VLAN ip address that we define when we want to > enable VLAN routing. Makes sense? Yes. berkid and I got it first time round too:) This is the design behaviour. Why would you want anything else? Use berkids solution which will looks pretty good to me if it's what you want. I mentioned the no keepalive not because I think it might be intrinsically better but because it might for some reason suit you better. It does work on some interfaces but I forget the details. I don't have access to a 4948 (or a 4500 which amounts to the same thing) to play with. -- Please sign the libel reform petition - no matter where you are in the world. Get others to sign too. Help to change these oppressive laws. http://www.libelreform.org/sign http://www.senseaboutscience.org.uk/index.php/site/about/476 http://www.libelreform.org/news/449-libel-reform-campaign-welcomes-jack-straws-commitment-to-libel http://www.libelreform.org/who-is-silenced http://www.libelreform.org/our-report/key-findings-of-report If your writing can be read in England or Wales you can be sued here. If you get sued, *you* have to defend yourself. You are assumed to be defamatory unless you can prove otherwise. Legal costs can be £Ms. Of course if you are in New York state you are explicitly protected by the "The Libel Terrorism Protection Act". Some other US states have similar protection.
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