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Beginner

Single vlan with multiple gateways

So here is a question.  I want to trunk the same vlan/subnet together between three geographically separated sites.  Lets say vlan10 associated to subnet 10.1.1.0 /28.  

 

Obviously I can create a single routed SVI interface at SiteA with IP address 10.1.1.1 /28 to act as the routed gateway for all three sites but then if a device on vlan 10 at SiteB wishes to speak to a device on Vlan 20 also at SiteB, it must first send it's traffic over the trunk to it's Gateway at SiteA.  Then from SIteA be routed back to SiteB.

 

So rather then do this, can I simply set up at all three sites a routed SVI Gateway for the Vlan10 subnet? 

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VIP Advisor

Re: Single vlan with multiple gateways

Hello

That would be a waste of network BW just so to communicate between a vlan on the same site.

How are these sites connected at present?



kind regards
Paul

Please don't forget to rate any posts that have been helpful.
Beginner

Re: Single vlan with multiple gateways

Exactly, which is why I do not want a single SVI for the subnet spanning multiple sites.  I want an SVI gateway at each of the three sites for the shared subnet.  

For this topology within our network the sites would be connected to one another fully meshed over a Layer 2 ELAN network. 

Rising star

Re: Single vlan with multiple gateways

use HSRP with the same vip and group but different authentication between sites
Beginner

Re: Single vlan with multiple gateways

Can HSRP support a secondary virtual IP on top of 3 real IP's?  I've only seen it done with 2 real IPs.  And if so, in HSRP you have a priority so the subnet traffic for Vlan10 would still use only one of the three sites as it's gateway which I want to avoid for the aforementioned waste of BW.

Rising star

Re: Single vlan with multiple gateways

not secondary!

just run hsrp on three sites with the same virtual ip and hsrp group but use different authentication.
Beginner

Re: Single vlan with multiple gateways

Sorry I meant to say Standby IP.  Not Secondary.  So are you saying use the same Stanby IP at all three sites?  Because that still requires setting one Standby with a priority greater then the Standby IP at the other two sites which means I'm back to traffic still only using the gateway at one site.

Rising star

Re: Single vlan with multiple gateways

all three must be active
Beginner

Re: Single vlan with multiple gateways

I tnink your talking about Gateway Load Balancing Protocol (GLBP) where you have multiple Gateways all active.  HSRP always acts Active/Standby.

 

Rising star

Re: Single vlan with multiple gateways

I'm talking about HSRP

If you can you may run mpls + evpn and have anycast gateway.

If you cannot so try this trick with hsrp.

site 1
!
interface Vlan50
ip address 10.10.50.2 255.255.255.0
standby 50 ip 10.10.50.1
standby 50 authentication text SITE_1


site 2
!
interface Vlan50
ip address 10.10.50.3 255.255.255.0
standby 50 ip 10.10.50.1
standby 50 authentication text SITE_2


site 3
!
interface Vlan50
ip address 10.10.50.4 255.255.255.0
standby 50 ip 10.10.50.1
standby 50 authentication text SITE_3

Beginner

Re: Single vlan with multiple gateways

Okay, let me lab that up.  I havent used authentication with HSRP before so I'm intrigued.  Thanks!

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