Subnets between core and access/distribution layers & routing between layers

I'm seeking out advice on connecting multihomed access & distribution devices back to a redundant core. Currently I'm working with a mix of methods.

1) A /28 or /27 VLAN was created on each core router to contain the aggregate links to the lower layered devices. The access/distribution devices have a L3 interface in this subnet.

2) A /30 is used between the core routers and the access/distribution layer devices.

3) A /29 with HSRP is used across the core routers on L3 VLAN interfaces and across the Ethernet interfaces on the access/distribution devices. Each core router has VLAN with a L3 address in the /29 and a common standby IP also in the /29. The access/distribution layer device has 2 Ethernet links back to the core that are 1Q trunks. That VLAN has a L3 address in the /29. This only works on a few devices, namely switches used for aggregation or routers with L2 ports like ENET HWICs.

I'm trying to figure out what the best approach is in this service provider environment. I personally favor #2. I believe this fits in better with a clean hierarchical IGP. I'm moving from OSPF to IS-IS in the very near future and would like to better utilize areas than they have been in the past (OSPF area 0 is touching every single device). #1 would make it difficult to separate IS-IS areas I think, especially if I use the VLANs for inter-connection VLANs for more than one type of device that should be in separate areas.

IPs aren't a concern. We're migrating from a public to a private IP infrastructure for the heart of this service provider. This will make ARIN happy.

On a related topic, I'm also soliciting advice on the basic configuration moving forward for edge and aggregation devices. Like I said earlier, we're moving to a pure IS-IS environment with a redundant core. All devices will be multihomed to the redundant core routers. All devices whether it be an access server, router terminating ATM PVCs for DSL, or a pair of aggregation switches that mulithome CMTSs will be running IS-IS and will be advertising the local routes back to the core (some with summarization like the access servers and ATM routers). The access/distribution layer devices are set up in one of 2 ways right now. Either their default route is originated in the IGP or they use a static default route (and in some cases still receive an default route from the IGP but don't use it). Should I originate a default route and remove the static default, should I use the static default route, or should I have a higher cost static route as a backup (rather useless I think)? Is there a best practice on this one that I can cite?

I just thought of another quick question. Do many people use (or find useful) 1Q trunks in a service provider network? I only have 2 1Q trunks in this entire network. Personally I would rather use L3 routing between capable devices wherever possible. I suppose if I use a pair of switches for aggregation (EMI code on 3750s or 4948s for example) I could use a pair of 1Q trunks between then for HSRP purposes. Do any other uses come to mind?

Thanks J

Reply to
Loading thread data ... Forums website is not affiliated with any of the manufacturers or service providers discussed here. All logos and trade names are the property of their respective owners.