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I have a situation that needs some clarification.

I have three sites (1,2,3). The core switch do Inter-vlan routing. Site 1 and 2 must access the internet via ISP1, while site 3 will access internet using ISP2. All switches are Catalyst 3750. However, only the CORE is acting as layer 3 and the rest of the switches are L2. How do I make all clients in site 3 to access their own internet (ISP2) while still participating in inter-vlan routing with the core.

To clarify this, for e.g. vlan 10 in site 1 and 2 will access ISP1 and vlan 10 in site 3 will access ISP2. Inter-Vlan routing is working perfectly, but how to I restrict clients in site 3 to only access ISP2?

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    What is the core switch model and configuration?
    – Ron Maupin ♦
    Jan 25, 2018 at 3:01
  • All switches are CISCO Catalyst 3750G. However, only the core is L3 and the rest are L2.
    – user3630837
    Jan 25, 2018 at 3:04
  • You need to edit the question to include the core switch configuration.
    – Ron Maupin ♦
    Jan 25, 2018 at 3:05
  • When a host in Site 3 sends a packet to the internet, it looks as if the packet will first reach the Site 3 L2 switch, then go to the Core router, then get routed back to the Site 3 Switch and then goes to ISP2 over the Meraki. Is my understanding correct?
    – mere3ortal
    Jan 25, 2018 at 3:18
  • @mere3ortal Correct
    – user3630837
    Jan 25, 2018 at 3:21

2 Answers 2

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You can use Policy-Based Routing (a route-map with an access-list):

  • Match all internet traffic from Site3 subnet.
  • Set the IP address of ISP#2 as next-hop.

The access-list for this route-map should deny all traffic from Site3 to Site1&2, and permit traffic from Site3 to the Internet.

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  • You may want to warn that PBR will punt to the CPU.
    – Ron Maupin ♦
    Jan 25, 2018 at 14:33
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By default policy based route will have priority on general route .. To fullfill your requirement PBR is best possible solution .

Route all vlan 10 traffic through ISP1 firstly . Then after further configured policy based routing in layer3 switch

Source as== site3 host address Destination as = ISP 3

PBR configuration in layer3 switch will forward site3 traffic to ISP3 .

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