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Routing with the 4108

Chris Bullock_1
Frequent Advisor

Routing with the 4108

I have drawn a complete blank. I currently have a 4108 with 3 VLANS, vlan 1 = vlan 2 = vlan 3 = What I have drawn a blank with is that we want to connect to the facility next door which has of coarse different subnets, we want to connect to them via fiber from our 4108 to their Cisco layer 3 switch, my confusion is how can I do this? Can I assign my fiber inerface with an IP address? I know that I can give VLANs IP addresses but my question is if I can't give my interface an IP address how can I route to that network? What we are planning to do is create a random network address to route the packets over that neither of us is using with only 2 IPs, one on my side of the fiber and one on the remote side.
Mohieddin Kharnoub
Honored Contributor

Re: Routing with the 4108

Hi Chris

Simply create a Vlan for the purpose of routing say Vlan4 and give it an IP (example), and untag the port connects to the Cisco switch,
Now on the cisco switch you have 2 options:

Enable the port connected to the 4100 switch from cisco side to be a L3 Router interface:

cisco(config)#interface fast 0/1 (assume port 0/1 connect to the 44100 switch)
cisco(config-if)#no switch-port (convert this port to be L3)
cisco(config-if)#ip add
cisco(config)#ip routing -- enable ip routing
cisco(config)#ip route -- configure a static route to the 10 networks with Vlan5 ip address as gateway on the 4100 switch from the cisco side
cisco(config)#show ip route -- to verfiy your routing table with the static one also

Now configure a static route for all cisco vlans with gateway

create Vlan5 on the 4100 with ip address say and untag the fiber port with this vlan5 then enable ip routing
and on the cisco side do the same:
cisco(config-if)#switch-port mode access
cisco(config-if)#switch-port access vlan 5
cisco(config)#ip routing

then add a static routes on both sides.

Good Luck !!!
Science for Everyone
Trusted Contributor

Re: Routing with the 4108

You should trunk (Cisco-wise) your 3 VLANs over the fiber link to the Cisco L3 device, and do routing there (I tried routing on the 4108 and it was BAD!).

For this you will need to define the 3 VLANs on the Cisco device; see what 802.1Q VLAN IDs were assigned to the VLANs when you created them on the Cisco (they usually call these IDs "VLAN ISL ID"), and use the SAME 802.1Q VLAN IDs on the 4108 for the corresponding VLANs; e.g. 5, 6, 7 (don't worry: it is easy to change these numbers on the 4108)

Remove the IP addresses from the 4108 VLAN interfaces and put them on the Cisco VLAN interfaces. I assume that routing is already taking place on the Cisco. I don't suppose that you REALLY have 65500 computers per subnet, so you could use /24 (gives you 254 usable IPs per subnet) or /23 (510 IPs) for subnetting.

(I would create a 4-th VLAN, just for the purpose of switch administration, and trunk this also, and put an IP on this VLAN for all switches. I would use the DEFAULT_VLAN for this purpose, who has 802.1Q ID = 1)

On the 4108 untag VLAN1 and tag VLANs 2 and 3 for the fiber port going to Cisco. Let's assume you have 1000Base-LX transceivers at both ends.

On Cisco:
#conf t
config#interface GigabitEthernet1/0/28
config-if# description "To 4108 port A1"
config-if# switchport trunk encapsulation dot1q
config-if# switchport trunk allowed vlan 5-7
config-if# switchport mode trunk
config-if# switchport nonegotiate (if you set 1000FDx on 4108 port A1)
config-if# speed nonegotiate (if you set 1000FDx on 4108 port A1)
config-if# flowcontrol receive on (if you set Flow Control = Enable on 4108 port A1)

Hope this helps