06-11-2019 02:47 AM
I have a l3 switch (3850) to a ISP router which has built in redundancy (fibre and wifi external connecting) managed by the ISP.
The l3 switch is in a stack of 2 and I want to add an additional link to the router for hardware redundancy.
What config will be need based on the diagram below?
06-11-2019 03:16 AM
Hello Merlin,
>> The l3 switch is in a stack of 2 and I want to add an additional link to the router for hardware redundancy.
The additional link should be taken from switch member 2 something like
gi2/0/16
However, to understand if you can add a second link to the ISP router you should provide some more info:
what type of IP subnet is currently used between your C3850 switch and the ISP router?
it is a public network like the one in your network diagram ?
What is the subnet mask?
If it is a public IP subnet with /30 subnet all you can do is to configure a L3 port channel with member links the two physical ports on your stack gi1/0/16 and gi2/0/16.
Be aware of the following:
a) the L3 configuration on gi1/0/16 the current used link should be removed and placed under the interface port-channel.
b) you need to work with the ISP tech support in order to have them to configure it for port channeling (if supported by the router)
If the ISP router does not support port channel, you would need to ask a second public IP subnet /30 to the ISP to use on the second link as a routed indipendent link.
In this case you will have two default routes pointing to the next-hops in current and new subnet.
Note: the ISP can require an additional fee for the new public subnet.
Hope to help
Giuseppe
06-11-2019 05:28 AM
06-11-2019 06:16 AM
Hello Merlin,
I don't understand the provided show output.
Is this the output of show cdp neighbors or show lldp neighbors ?
Why we see two different neighbors out of port gi1/0/16 the current link ?
IP address: 151.249.1.1
>> Interface: GigabitEthernet1/0/16, Port ID (outgoing port): vrrp1
>> IP address: 151.249.1.2
>> Interface: GigabitEthernet1/0/16, Port ID (outgoing port): bridge0
The first line that mentions VRRP (the standard equivalent of HSRP) makes me think that the ISP routers can be two and not only one. (unless VRRP is configured as a preparation to add a second router)
The second entry tells about a bridge0 interface that makes me think the ISP router is using a feature like bridge domains.
If L3 port-channel configuration is possible on the ISP router (and it is only one device) I would go this way.
Hope to help
Giuseppe
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