Cat9k to 1920 Router GLBP Uplink

[Dejan Uskokovic]

Hello all,

How can I or even could I, create a port channel on a pair of cisco 1920 or 1921 running GLBP to allow redundant links from a switch stack that connect to routers for equal link utilization?

Is a port Channel solution to it or a sub-interface port-channel, or...?

Switch stack is c9k (Everest 16.6.2) and a pair of cables connect them four.

cabling:
c9k stack member 1 gi1/0/1 to 1st 1920 gi0/0/0 and
c9k stack member 2 gi2/0/1 to 2nd 1920 gi0/0/0

config:
c9k stack member 1 gi1/0/1 access vlan AAA
c9k stack member 2 gi2/0/1 access vlan AAA

interface vlan AAA
IP address A.B.C.1

1st 1920 gi0/0/0 IP A.B.C.252
2nd 1920 gi0/0/0 IP A.B.C.253

GLBP IP A.B.C.254

Thanks,

[paul driver]

Hello
Your rtrs would each an lan facing interface that is connected to the switch stack, The switch stack would have SVI interface with an ip address that share the same address range as the routers lan facing interfaces and a default route or default-gateway pointing to the GLBP virtual ip address on the routers.

Naturally you would want resiliency for you upstream connections but below just shows a basic glbp example on the lan facing devices

Example:
rtr1

in x/x
description Lan facing
ip address 10.1.123.252 255.255.255.0
glbp 1 priority 115
glbp 1 prempt
glbp 1 ip 10.1.123.254

rtr2

in x/x
description Lan facing
ip address 10.1.123.253 255.255.255.0
glbp 1 prempt
glbp 1 ip 10.1.123.254

switch stack
int vlan 123
ip address 10.1.123.251 255.255.255.0
exit
ip route 0.0.0. 0.0.0.0 vlan 123 10.1.123.254

int x/x
description rtr1
switchport mode access
switch access vlan 123

int x/x
description rtr2
switchport mode access
switch access vlan 123

[Dejan Uskokovic]

Well said Paul Driver and Top Post!

This is exactly what I'm having on; the only thing that bothers me is the spanning-tree that will ultimately kick in and assign different cost to them two uplinks of 1Gbps, I believe the cost of 4 to the 1st one and 19 to the second leaving me with just one passing traffic up to the routers? They are sitting in the same vlan and not bundled up in a port-channel;

Anyhow, soon I will implement it and find out.

Thanks again and I will come around again and rate your post top.

Cheers

[paul driver]

Hello

---

@Dejan Uskokovic wrote:

Well said Paul Driver and Top Post!

This is exactly what I'm having on; the only thing that bothers me is the spanning-tree that will ultimately kick in and assign different cost to them two uplinks of 1Gbps, I believe the cost of 4 to the 1st one and 19 to the second leaving me with just one passing traffic up to the routers? They are sitting in the same vlan and not bundled up in a port-channel;

---

Stp is a layer 2 loop avoidance feature it will have no bearing on any L3 glbp routed interfaces.

[Dejan Uskokovic]

Hi

I agree that an stp is a layer 2 instrument but where did we turn the interfaces into a layer 3 ones at the switch side?

BR

dejan

[paul driver]

Hello

You will have a SVI on the switch and then the two rtrs lan facing interfaces connected to access ports on switch stack assigned to the vlan of the L3 SVI.

[Dejan Uskokovic]

Hello

You will have a SVI on the switch and then the two rtrs lan facing interfaces connected to access ports on switch stack assigned to the vlan of the L3 SVI.

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thanks, that makes very much sense indeed; i am going to implement it and post here what the result was, thanks again.

[Dejan Uskokovic]

Hello

You will have a SVI on the switch and then the two rtrs lan facing interfaces connected to access ports on switch stack assigned to the vlan of the L3 SVI.