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loopback question [Solved]


I have the following configuration.

one 3560 switch with 3 vlans, on interface 0/1 I have configured a trunk with 802.1q encapsution to two 6850 Alcatel-luccent switch (RIP is enable between the Alcatel switch).

I have configured 3 loopback interface on each switch for vlan management

From Alcatel-lucent switch I can ping the loopback on each Alcatel switch but not the loopback interface of the 3560.

The 3560 switch cannot ping the loopback of Alcatel switch, why?

someone have an idea to solve my problem?


Community Member

It doesnt sound like your 3560 is participating in the routing and is acting more as a layer 2 transport between the two switches that are.

Community Member

Sorry, I don't understand your reply.

3560 is layer 3 swith like the Alcatel switch (L2+ which can do routing like RIP/static route and other).

To join the loopback from the Alcatel switch it's necessary that the 3560 is layer 3?

Community Member

I am not sure I have a clear picture of the network you have, but based on how I read your post you have two devices that are participating in rip routing "the alcatels". Therefore they understand where the other addresses live, based off the route advertisements, and know where to send the icmp requests.  How is your 3560 participating in the routing? Do you see anything in the routing table of your Alcatels for the 3560s loopback and vice versa. I'm just wondering if you need to enable routing on the 3560. Since you are using loopbacks they would need to be advertised out for the other devices to know how to reach them or static routes need to be added.

Community Member

I try to explain the topology of my network

CISCO 3560 (backbone)-> Alcatel 6850 (SWITCH13)-> Alcatel 6850 (SWITCH12)

There are a trunk with 802.1q encapsulation between 3560 and Alcatel 6850 (SWITCH13) and the RIP protocol between Alcatel 6850 (SWITCH13) and Alcatel 6850 (SWITCH12)

From Alcatel 6850 (SWITCH13) can ping all vlan on the 3560 but not the loopback interface.

Loopback0 : on 3560
Loopback0: on Alcatel 6850 (SWITCH13)


backbone#show ip route
Codes: C - connected, S - static, R - RIP, M - mobile, B - BGP
       D - EIGRP, EX - EIGRP external, O - OSPF, IA - OSPF inter area
       N1 - OSPF NSSA external type 1, N2 - OSPF NSSA external type 2
       E1 - OSPF external type 1, E2 - OSPF external type 2
       i - IS-IS, su - IS-IS summary, L1 - IS-IS level-1, L2 - IS-IS level-2
       ia - IS-IS inter area, * - candidate default, U - per-user static route
       o - ODR, P - periodic downloaded static route

Gateway of last resort is not set is variably subnetted, 2 subnets, 2 masks
C is directly connected, Vlan101
C is directly connected, Loopback0
C is directly connected, Vlan1
C is directly connected, Vlan100


SWITCH13-> show ip route

+ = Equal cost multipath routes
* = BFD Enabled static route
Total 6 routes

  Dest Address      Subnet Mask       Gateway Addr      Age       Protocol
------------------+-----------------+-----------------+---------+-----------          26d 5h  LOCAL      05:15:08  RIP       04:42:57  LOCAL           35d10h  LOCAL        27d 1h  LOCAL       26d 5h  LOCAL

The CISCO 3560 is directly connected by a trunk on the Alcatel 6850 (SWITCH13), I can ping all vlan but the loopback, it's a routing problem?

Community Member

Yes, that is correct. Your cisco switch does not know about the Alcatels loopbacks and they have no knowledge of his. Looks like your common vlan between the switches is vlan 1. On the 3560 you could enable rip routing add vlan 1 (  and add your loopback to it in order to advertise it out and learn about the Alcatels loopbacks. There are other ways using static routing but they would require more of an explanation.

Host networks /32 need to be advertised.

Community Member

Thank you for this explanation, I begin to understand.

I don't want to enable the RIP on the 3560, I prefer to use a static route and I have a problem with that.

If I'm not saying stupidity, loopback0 on 3560 is directly connected the loopback0 of Alcatel 6850 (SWITCH13), I can understand that is not possible from 3560 to ping the loopback of Alcatel 6850 (SWITCH12) but why I can not ping the loopback0 directly connected?

If I add a static route on the 3560 which gateway? This address is not reachable.

Community Member

From the 3560 you can see in the route table that is doesn't know about that address. So when you ping from your 3560 it has no idea where to send traffic. Now if you have a vlan that is common between the two switches (Vlan1), and if they both have interfaces in that vlan you could point static routes to each others loopbacks with the next hop of those vlan 1 interfaces.

Does that help?


Community Member

Todd, many and many thank again.

I have add these two route on the 3560

ip route

ip route

Now, everything works perfectly.