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newf5learner's avatar
newf5learner
Icon for Nimbostratus rankNimbostratus
Aug 19, 2016

Forwarding L2 & Forwarding IP virtual servers - when to use them?

I have been looking at various posts related to forwarding L2 and forwarding IP virtual servers.

Forwarding L2 - 'will have the same IP address as that of the node in the vlan'

For situations where a proxy should be used to bridge two different Ethernet collision domains, a layer 2 forwarding virtual service an be used.

Lets say, I have a node 10.20.20.20 accessible on ssh. Can I configure a forwarding L2 VIP with Ip address as 10.20.20.20 and listening on port 22 with SNAT automap ?? It didn't work though!

self-IP configured with port lockdown as 'allow all'while testing the above scenario is 10.20.20.25 and the default route I had was 10.20.20.1 (router)

can someone help me understanding the concept behind this VIP type and the usage.

Reference : https://devcentral.f5.com/articles/back-to-basics-the-many-modes-of-proxies

Forwarding IP: 

'For simple packet forwarding where the destination is based not on a pooled resource but simply on a routing table, an IP forwarding virtual service turns your proxy into a packet layer forwarder.'

Please correct me if my understanding is wrong with this also. 😞

lets say, the Big-IP is connected between two L3 switches, Where switch-1 has a static route for Network X(10.10.x.0/24) pointed to 10.10.x.253 and the self-IP address on the F5 is (10.10.x.254). Switch-2 has all the hosts connected on the network X. And switch 1 doesn't have any other routes and no other ways to communicate than through the F5. Now I configure a forwarding IP virtual 10.10.X.0/24 : * (any port) with SNAT automap. On the f5, assuming that my default route is a vlan IP on switch-1, Should I also have a f5 route entry configured for network X? network 10.10.x.0/24 -- gateway -- 10.10.x.252 (L3 vlan IP oon switch-2) ? Not sure if this works, but let me know if the concept is appropriate.

Please suggest if my understanding with these virtual server types are correct and let me know where and how these are useful.

application delivery
LTM
TMOS

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  • boneyard's avatar
    boneyard
    Icon for MVP rankMVP
    Aug 21, 2016

    L2 is L2, so it is useful when you have the big-ip in L2 mode, so inline between two switches which force the traffic on L2 level through the box.

     

    forwarding IP would be useful for pool members behind the big-ip as default to get external access. you configure a forwarding IP server on the pool member VLAN and have a default route towards the internet. servers send there requests towards the big-ip where the forwarding IP virtual server picks it up looks at the routing table and sends it forward there.

     

    you need to setup your routing on the big-ip as you would on a router, the forwarding IP virtual server follows the routing table it doesn't create new routes or such.