The IP on my Catalyst 2950 switch is missing

[gafsonmrray]

Hi, I have 3 Cisco Catalyst 2950-24 on my small network. One with IP 192.168.0.6 is connected to another one with IP 192.168.0.1 which in tend connects to my DHCP/AD/DNS/RRAS server via NIC 192.168.0.3. The third switch is on a different subnet with IP 192.168.10.7 but also connected to the same server via NIC 192.168.10.3. From the onset, everything was working perfectly well until i realised a couple of mnths back that I cannot reach the third switch (192.168.10.7) from my DNS/DHCP/AD?RRAS server. I can also not reach it from any of the PCs on either subnets (192.168.10 and 192.168.0). However, the PCs connected to this particular switch communicates with every other PC on those subnets and vice versa.

My worry is that I am unable to manage this 3rd switch (192.168.10.7) because it's IP is "lost". I scanned the network for any available IP that might have been mistaken set on it but have gotten nothing.

How can I get the IP of this switch (without resetting it) in order to be able to manage it?

[cadet alain]

Hi,

Just ping the broadcast address froma machine in the same subnet and any switch in this subnet will reply if there is no ACL configured.

You can also try a sh cdp nei detail from the other switch on the same link.

Regards.

Alain.

[gafsonmrray]

Thanks, i tried these options but they didn't work.

[cadet alain]

Hi,

So the SVI is up/down or admin down/down but I would dismiss former option otherwise you wouldn't be able to communicate between ports in this VLAN so I think you'll have to go physically to this switch and issue a sh ip int br | i Vl to see the status of your SVI( maybe it was also deleted from the switch).

Regards.

alain.

[CHRISTOPHER LARSON]

The 2950 does not do any routing from what I understand, so I do not think you will be able to route between subnets easily using these switches. You could turn your dhcp server into a router as it has access to both subnets, but if it were me, I would want something L3 to route between my vlans. I would use the 2950 as access layer switches and trunk/uplink to my L3 switches that route between the vlans.

Even then though, I am not sure you can use a dhcp helper address in the 2950. So even then you might need an interface from the DHCP into each switch. If they had more capability, you could hang your DHCP wherever you want and add dhcp helper-address and get to the DHCP from anywhere with only 1 interface on the DHCP.

[gafsonmrray]

Thanks Chris, will try your suggestion when I get to work on Monday and get back to you.

[hobbe]

Hi

its quite simple.

you take the blue serial cable and connects the blue cable to the 2950 switch consol port and the other end in the computer.

use a program such as putty or hyperterminal that supports serial ports and connect to the switch.

you then login to the switch and do what you need to do to enable management of it.

Good luck

HTH

[Steven Williams]

2950 are layer 2 switches only. They do not use SVI's. Vlans can be assigned IP addresses for management purposes only. You will need a layer 3 device like router on a stick. The default gateway on the 2950's should have the IP of the router or layer 3 device.

[Peter Paluch]

Steven,

By definition, any interface VLAN X is a SVI. Just on 2950, they are simply management interfaces - virtual connections of the internal CPU to a particular VLAN with a respective IP address, without an ability to route between VLANs.

VLAN can never be assigned an IP address. VLAN is a virtualized broadcast domain, and just as a broadcast domain does not have an IP address per se, so cannot VLANs have IP address. The IP addresses are assigned to SVIs.

This may appear as a nitpicking and word hunting but the precision in expressing oneself is very important in the networking field. Absolutely no offense intended.

Best regards,

Peter

[Steven Williams]

I would tend to think that when in a room with a few other network admins like myself, and I mentioned SVI, we would all be on the same page with L3 connectivity. Just my opinion.

[Peter Paluch]

Hi Steven,

Well, yes, I agree that the SVIs are mentioned most often in relation to Layer3 switching. However, even the Configuration Guide for 2950 Catalyst series switches calls the interface VLAN as SVI. Also, the IOS Interface and Hardware Component Configuration Guide states regarding the SVIs:

Switched Virtual Interface

A switch virtual interface (SVI) represents a VLAN of switch ports as  one interface to the routing or bridging function in the system. Only  one SVI can be associated with a VLAN, but it is necessary to configure  an SVI for a VLAN only when you wish to route between VLANs,  fallback-bridge nonroutable protocols between VLANs, or to provide IP  host connectivity to the switch. By default, an SVI is created for the  default VLAN (VLAN 1) to permit remote switch administration. Additional  SVIs must be explicitly configured. You can configure routing across  SVIs.

Of course, this has to be interpreted with a proper relation to the switch capabilities, i.e. a Layer2 switch cannot provide routing functions, but the idea is here: it is an interface of the internal CPU towards a particular VLAN, in other word, the host connectivity of the switch to the particular VLAN.

Best regards,

Peter