Active-Active Edge topology

[John.Mayer]

Hi 

I have the following scenario and little confused about the technology and topology that need to be used 

RTR1 and RTR2 are the service provider routers (CE), and the provider informed us that they have an active-active connection via BGP.

The question is, how can I establish an active-active connection between my L3 switch and these two routers? In the past, for active-standby connections, I have used EIGRP or HSRP to direct traffic to the active device. However, now I am considering using GLBP and finding it confusing.

[M02@rt37]

Hello @John.Mayer 

Follow your service provider requirements. Establish BGP peering between your L3 switch and both RTR1 and RTR2. Enable BGP multipath on your L3 switch. This allows for load balancing across multiple BGP paths.

If both RTR1 and RTR2 are advertising the same routes with equal metrics, the L3 switch can perform ECMP and distribute traffic across both paths.

Which L3 switch is it ?

[DanielP211]

Hello,

You will have to setup routing between L3 switch and the RTR's and setup ECMP. I wouldn't go with GLBP because it's rarely used.

BR

[paul driver]

Hello
Could you elaborate a little on your network.

• Type of switch
• ISPs ( as they the same provider )
• What routing do you have between the rtrs and switch
• Are you receiving a full internet/partial route table or just default route.

As you dont state what routing protocol to have between the rtrs and the switch, ruining bgp between then will NOT provide you ECMP by default due to its best path section process however it can be enabled although you may need to additionally relax the aspath selection if the ISPs s are from different bgp domains.

Running an IGP (ospf/eigrp) can provide you load sharing but again it depends on what protocol you choose and you requirements

Lastly you need to make sure you dont become a transit path between the ISPs which is possible when you are multihoming

[balaji.bandi]

RTR1 and RTR2 are the service provider routers (CE), and the provider informed us that they have an active-active connection via BGP.

RTR1 and RTR2 are the service provider routers (CE) - this means you do not have any access to configure by yourself - you always need to rely on provider to make changes ?

you also need to check with provider, what kind of config they can change offer you , IGP / iBGP here ?

As asked other post you need to provide what  model / IOS  capabilities of the switch ? what kind of Routes you getting from Provider ?

For me OSPF is easy method - if the links are equal for LB between the Links, or if you have good switch you run the BGP also here.

But you provided up to Switch, (the switch itself single point of failure here)  on the LAN side  - any other switches or end device directly connect to switch ?

if you still looking to go with GLBP look at below example  and use case :

https://www.cisco.com/en/US/docs/ios/12_2t/12_2t15/feature/guide/ft_glbp.html#wp1027184

[MHM Cisco World]

It depends 

-you use l2 between SW and router then use glbp

- you use l3 between SW and router use igp or default route

MHM

[Paw_Paw]

Good Morning

When the routers are devices from the ISP, they do not allow you to choose the technology. Ask your provider what they prefer.

The technologie choices are provided above but I assume you are not able to choose which one you want.

regards

[John.Mayer]

Hello everyone,

I have a stack of Catalyst 9300 switches with the network advantage license and IOS-XE 17.6, and for service provider routers, I believe they should be ISR44xx. Both connections are from the same provider. 

As many of you have pointed out, I don't have access to the CE routers, but I know that they advertise the same routes and use BGP. I am currently requesting more information from the provider about their technology and topology. 

I am considering using either EIGRP or OSPF between the core switch and CE routers. I was thinking of using OSPF for active-active scenarios and EIGRP for active-passive scenarios with different subnets. 

What are your thoughts on this approach?

[balaji.bandi]

 I was thinking of using OSPF for active-active scenarios and EIGRP for active-passive scenarios with different subnets. 

Since you are in touch with Provider - You need to come to agreement with provider configure OSPF as open standard - that is easy for them to configure their end.(if they agree)

i suggest to use OSPF for ECMP  (if both the links are same speed) even using OSPF you can have equival load-balance or active-standby (using cost or route-maps one over other connection.) - but as you mentioned ISP doing LB Active- active BGP - you may have return traffic from any Router. (since BGP is not in your control to play preference).

is there any NAT involved here ? is this connections to Internet or just WAN between Offices ?

[John.Mayer]

I was informed by the provider that they want to configure EIGRP between our CE and core switch. I'm wondering whether it's possible to have Active-Active links on EIGRP or if I need to use route-maps to direct certain traffic to CE1 and other traffic to CE2.

[M02@rt37]

Hello @John.Mayer 

EIGRP supports load balancing across multiple paths, allowing for Active-Active links. You can achieve this by adjusting the bandwidth or delay metrics on the interfaces. However, keep in mind that EIGRP might still prefer one path over another based on its composite metric. Route-maps could be used for more granular control if needed, directing specific traffic to CE1 or CE2.

[balaji.bandi]

EIGRP works for you. EIGRP have many ways you can do preferred path selection - playing with delay

You can also use Route-map  with distance per subnet 

there are couple examples as below : 

https://www.cisco.com/c/en/us/support/docs/ip/enhanced-interior-gateway-routing-protocol-eigrp/221548-configure-eigrp-to-influence-path-select.html#anc14

is there any NAT involved here ? is this connections to Internet or just WAN between Offices ?

[MHM Cisco World]

You can not access CE' ask admin about his opinion about using l2 or l3 between CE and your SW.

MHM

[Paw_Paw]

We have always configured HSRP for the customers. If routing protocol, then BGP. We did not configure OSPF with customer.