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Rajeev's avatar
Rajeev
Icon for Nimbostratus rankNimbostratus
Oct 30, 2023
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Would Auto last hop feature work with multi vrf environment on F5

Hi Team, this is regarding auto last hop feature, If we have two vrf on upstream device(switch) and the traffic is coming on respective VIPs on F5 , we have auto last hop feature  enabled on F5, then would the return traffic land on the respective vrfs on switch, from the VIPs ?

We have only one default route on F5 which is pointing towards the upstream switch and this IP is in global ( I mean the next hop IP is not in any VRF).

Do we need to do any work around for multi vrf return traffic?

Or the Auto last hop feature will take care automatically for the same ?

For example setup is like :-

Upstream switch:-

vlan 301

30.30.1.1/24

Vrf A

Vlan 101

IP:- 10.10.1.1/24

Vrf B

Vlan201

IP :- 20.20.1.1/24

F5 setup :-

VIP :- 10.10.1.5 --- ( pool members:- 1.1.1.5 and 1.1.1.6) 

Servers gateway:- Floating self IP (1.1.1.1)

VIP :- 20.20.1.5--( pool members:- 1.1.1.12 and 1.1.1.13)

Servers gateway:- Floating self IP ( 1.1.1.1)

On F5, Default gateway is pointing towards IP 30.30.1.1 .

In this scenario auto last hop features will work or not ? 

Or we need to do some work arounds for return traffic from F5 to upstream device ?

 

Kindly suggest . Thanks 

application delivery
  • Niels_van_Sluis's avatar
    Niels_van_Sluis
    Oct 30, 2023

    In additon to what PSFletchTheTek wrote, Auto Last Hop only applies to traffic from clients towards the F5. For the traffic that goes from the F5 towards the pool members, the routing table is used. So, if I understand your network topology correctly this setup should work fine with Auto Last Hop enabled. The F5 will just return the packet towards the client to the same interface it came in at first. 

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  • PSFletchTheTek's avatar
    PSFletchTheTek
    Icon for MVP rankMVP
    Oct 30, 2023

    HI,

    Not totally sure on your network layout, but to try to help auto last hop looks at the mac of the incoming packet and makes sure it goes back to the same location, this is BEFORE it looks at the routing table.
    So its good if you have higher networks where traffic may come from different locations, it should go back to where it came from.

    The only issue here is, managing the default route on the return path of the external network.
    Comms will leave the f5 correctly, the issue is normally when it hits the higher router will it then default to a different path to the incoming traffic.

    We had to tweak our network design to make this work cleanly, but in our case it wasn't a difficult thing to change and has worked really nicely ever since!

  • T-Trust's avatar
    T-Trust
    Icon for Cirrostratus rankCirrostratus
    Oct 30, 2023

    Hello Rejeev,

    Could you please provide diagram ? but from concept last hop response from incomming request and return back

  • Niels_van_Sluis's avatar
    Niels_van_Sluis
    Icon for MVP rankMVP
    Oct 30, 2023

    In additon to what PSFletchTheTek wrote, Auto Last Hop only applies to traffic from clients towards the F5. For the traffic that goes from the F5 towards the pool members, the routing table is used. So, if I understand your network topology correctly this setup should work fine with Auto Last Hop enabled. The F5 will just return the packet towards the client to the same interface it came in at first. 

    • Rajeev's avatar
      Rajeev
      Icon for Nimbostratus rankNimbostratus
      Nov 13, 2023

      Thank you all for your support and solutions.I have tested auto last hop option and it is working as expected. Thanks All.