ISP layer 3 switch design

[WillscottCiscoGeek]

Hi,

I'm designing a small ISP network and I'm after some advise with routing when using a layer 3 switch.

I'm planning on terminating customer ethernet connections physically and logically on a 3750 switch. Each customer will be connected to a routed port on the 3750 and assigned a /30 for the basic point-to-point. Static routes will then be configured on the 3750 for the customer public IP address blocks. The 3750 will be uplinked to two core/edge 7200 using a /30 point to point links.

As I understand it the customer prefixes  should be advertised via BGP and not via IGP. If this is the case I will need to configure iBGP between the 3750 and core/edge routers but I'm concerned that the 3750 wont handle a full routing table which we have on the core/edge.

Is this the correct setup? Should we only advertise a default to the 3750?

An alternate design would be to terminate the customer connections on VLANs and trunk to the 7200 and configure subiterfaces on the 7200 instead. The customer prefixes can then be advertised into BGP on the core/edge instead?

Any thoughts?

[Simon Brooks]

Configure prefix list and route map to only advertise default route to 3750 on the edge and redistribute this to the customer routers respectively on the 3750. Advertise the customer prefixes up to the edge. You are correct. Is this just internet acces only out of your edge or are you routing across mpls to other customer sites? Multiple customers on same 3750 will sllow them to route between themselves, is this okay? Otherwise look at inter vrf routing using bgp where you only allow customers to access edge routes by the use of route target import and exports. That way all traffic will be routed to edge and back down to 3750 ig necessary. Unless your fine with customers using 3750 as transit between each other.


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[WillscottCiscoGeek]

Hi

Thanks for this.

Yes the 3750 is just providing internet access and yes we are happy with customers routing to each other via the 3750.

Is there any advantage using the 3750 to perform the routing instead of trunking to the 7200 and using subinterfaces instead?

[Simon Brooks]

Trunking up to 7200 is an option and that router would give you better processor power with routing, however it shouldn't be needed.  Just how many customers are you terminating on the 3750?  It will be able to cope with quite a few prefixes to be honest!  Then just have a default route for BGP advertised down to the 3750.

[usman198]

Hi Simon and wittscot,

In this scenerio you think i am a customer and want to use 3850 L3 on customer side for internet connection from ISP .

- should i use Layer 3 MPLS

- just default route to send traffic to uplink

i am not seeing nat on 3850 what other model should i use . i need  layer 3 10 gig interfaces.

does security feature on L3 switch would be enough to secure internal network

i am hosting SBC inside .

THX

Usman