DD2491 p Load balancing BGP. Johan Nicklasson KTHNOC/NADA

Transcription

1 DD2491 p Load balancing BGP Johan Nicklasson KTHNOC/NADA

2 Dual home When do you need to be dual homed? How should you be dual homed? Same provider. Different providers. What do you need to have in place to do dual homing? AS number PI vs. PA BGP?

3 Single provider You can do dual homing to the same provider. What kind of redundancy do we have in this setup? BGP does not load balance across multiple links.

4 Single provider What level of redundancy do we need? Do we need redundant routers? Do we need to connect to different POPs? What about the local loop? Can we load balance over redundant links? Maybe. In the previous example we could make use of an IGP to load balance packets over the two links. It is not likely that the provider wants to do that. A provider wants his edge to be as static as possible. What about different routers?

5 Single provider Redundant routers. We can loose 1 router and still be connected to the internet. If the ISP router dies our connections goes with it. The local loop may or may not be redundant.

6 Single provider Redundant routers and redundant POPs We can loose one of our routers and still have connectivity. We can loose one provider router/pop and still have connectivity. The local loop may or may not be redundant.

7 Single provider Dual homed to the same provider. We can have different levels of redundancy. Depending on our needs. Do we need BGP to dual home to the same provider? Even in the setup with 2 routers and 2 POPs we can use a static default route to get to the internet. We inject the default route into our IGP and the node will send it's traffic to the nearest exit point. Can the ISP load balance traffic to us?

8 Single provider If we use BGP on our connections to our ISP We must have an ibgp connection between our edge routers. We can still use a static default route to the internet. The provider can send us a default route via BGP. We can use MED, AS prepend or communities to try to get the ISP to send us traffic to different prefixes over different links.

9 Single provider If we get a full table from our ISP We need our hardware to handle ~ prefixes. We can use policies to have the traffic leave on different links depending on the destination. If we don't make our IGP aware of those routes we could end up with suboptimal routing, depending on the network topology.

10 Single provider Addressing and AS numbers The provider will assign IP address space to us. We don't have to have our own AS number. We can use a private AS, that have to be assigned to us by our provider. Private AS numbers are to The provider have to remove private AS's from prefixes on their ebgp peerings.

11 Dual providers Our address space becomes an issue. We need PI (Provider independent) space We need a public AS number. How to get an AS number will be covered later. BGP is a must.

12 Dual providers

13 Dual providers If we should use IP space provided by ISP A, /24 That /24 is just a portion of the space provided to the ISP by the RIR /19 We get ISP B to announce our /24 (most ISPs will never announce part of another ISP aggregate).

14 Dual providers

15 Dual providers Which ISP will attract all our traffic? Longest prefix match One solution to this problem would be to have ISP A announce /24 and /19.

16 Dual providers

17 Dual providers Another solution to this problem is to get Provider Independent (PI) IP space from a RIR (Regional Internet Registry). To use PI space will also make it much easier to switch ISP. With PA space the ISP owns the IP addresses you use. If you move to another ISP the first one will make you return the borrowed space.

18 Dual providers Load balancing the egress Using BGP attributes and IGP cost you can prefer one prefix set over one ISP and another set over the other ISP. This will not balance the load equally over the two upstreams. If you monitor your traffic patterns you could try to balance the load more.

19 Dual providers Load balancing the ingress Is it possible to use MED when dual homing with two IPSs? Is it possible to use AS prepend? How about announcing more specific routes to attract traffic? You have to have a good dialog with your ISPs when you are doing any kind of traffic engineering.

20 Symmetry/asymmetry and the internet When you have more the one way to reach a destination symmetry can not be guaranteed. Some hardware dealing with state and flow needs symmetry to work properly.

21 Symmetry/asymmetry

22 Symmetry/asymmetry We have to have traffic leaving a firewall return over the same one. We could use AS prepend. We could advertise more specific routes What if the firewalls exchanged their current flow and state tables?

23 Questions?