Repost: EBGP-Mostly Service Provider Network
Daryll Swer left a long comment describing how he designed a Service Provider network running in numerous private autonomous systems. While I might not agree with everything he wrote, it’s an interesting idea and conceptually pretty similar to what we did 25 years ago (IBGP without IGP, running across physical interfaces, with every router being a route-reflector client of every other router), or how some very large networks were using BGP confederations.
Just remember (as someone from Cisco TAC told me in those days) that “you might be the only one in the world doing it and might hit bugs no one has seen before.”
Repost: EBGP-Mostly Service Provider Network
Daryll Swer left a long comment describing how he designed a Service Provider network running in numerous private autonomous systems. While I might not agree with everything he wrote, it’s an interesting idea and conceptually pretty similar to what we did 25 years ago (IBGP without IGP, running across physical interfaces, with every router being a route-reflector client of every other router), or how some very large networks were using BGP confederations.
Just remember (as someone from Cisco TAC told me in those days) that “you might be the only one in the world doing it and might hit bugs no one has seen before.”
Public Videos: Service Insertion in EVPN Fabrics
In 2020, Lukas Krattiger ran a short webinar describing how to insert L4-L7 services into EVPN fabrics. The videos are now public, and you can view them without an ipSpace.net account.
BGP Labs: Advertise the Default Route
If you’re an Internet Service Provider running BGP with your customers, you might not want to send them the whole Internet routing table. Sending the regional prefixes and the default route is usually good enough.
BGP Labs: Advertise the Default Route
If you’re an Internet Service Provider running BGP with your customers, you might not want to send them the whole Internet routing table. Sending the regional prefixes and the default route is usually good enough.
FRRouting Claims IBGP Loopbacks Are Inaccessible
Last week, I explained the differences between FRRouting and more traditional networking operating systems in scenarios where OSPF and IBGP advertise the same prefix:
- Traditional networking operating systems enter only the OSPF route into the IP routing table.
- FRRouting enters OSPF and IBGP routes into the IP routing table.
- On all platforms I’ve tested, only the OSPF route gets into the forwarding table1.
One could conclude that it’s perfectly safe to advertise the same prefixes in OSPF and IBGP. The OSPF routes will be used within the autonomous system, and the IBGP routes will be propagated over EBGP to adjacent networks. Well, one would be surprised 🤦♂️
FRRouting Claims IBGP Loopbacks Are Inaccessible
Last week, I explained the differences between FRRouting and more traditional networking operating systems in scenarios where OSPF and IBGP advertise the same prefix:
- Traditional networking operating systems enter only the OSPF route into the IP routing table.
- FRRouting enters OSPF and IBGP routes into the IP routing table.
- On all platforms I’ve tested, only the OSPF route gets into the forwarding table1.
One could conclude that it’s perfectly safe to advertise the same prefixes in OSPF and IBGP. The OSPF routes will be used within the autonomous system, and the IBGP routes will be propagated over EBGP to adjacent networks. Well, one would be surprised 🤦♂️
OSI Layers in Routing Protocols
Now and then, someone rediscovers that IS-IS does not run on top of CLNP or IP and claims that, therefore, it must be a layer-2 protocol. Even vendors’ documentation is not immune.
Interestingly, most routing protocols span the whole seven layers of the OSI stack, with some layers implemented internally and others offloaded to other standardized protocols.
OSI Layers in Routing Protocols
Now and then, someone rediscovers that IS-IS does not run on top of CLNP or IP and claims that, therefore, it must be a layer-2 protocol. Even vendors’ documentation is not immune.
Interestingly, most routing protocols span the whole seven layers of the OSI stack, with some layers implemented internally and others offloaded to other standardized protocols.
netlab: Building Leaf-and-Spine Fabrics with the Fabric Plugin
netlab release 1.7.0 added the fabric plugin that simplifies building lab topologies with leaf-and-spine fabrics. All you have to do to build a full-blown leaf-and-spine fabric is:
- Specify the default device type
- Enable the fabric plugin
- Specify the number of leaves and spines in the fabric.
For example, the following lab topology builds a fabric with Arista cEOS containers having two spines and four leaves:
netlab: Building Leaf-and-Spine Fabrics with the Fabric Plugin
netlab release 1.7.0 added the fabric plugin that simplifies building lab topologies with leaf-and-spine fabrics. All you have to do to build a full-blown leaf-and-spine fabric is:
- Specify the default device type
- Enable the fabric plugin
- Specify the number of leaves and spines in the fabric.
For example, the following lab topology builds a fabric with Arista cEOS containers having two spines and four leaves:
Worth Reading: Things We Know about Network Queues
Every time someone tries to persuade you to buy (expensive) big-buffer data center switches, take an antidote: the Things we (finally) know about network queues article by Avery Pennarun.
Worth Reading: Things We Know about Network Queues
Every time someone tries to persuade you to buy (expensive) big-buffer data center switches, take an antidote: the Things we (finally) know about network queues article by Avery Pennarun.
Public Videos: Routing Protocol Convergence
All Routing Protocol Convergence videos from the How Networks Really Work webinar are now public. Enjoy!
BGP Labs: Stop the Fat-Finger Incidents
Last time, we discussed the first line of defense against fat finger incidents: limiting the number of BGP prefixes your router accepts from a BGP neighbor. However, you can do much more without deploying customer-specific filters (which might require a customer database) or ROV/RPKI.
You can practice the default filters you should always deploy on EBGP sessions with your customers in the Stop the Propagation of Configuration Errors lab exercise.
BGP Labs: Stop the Fat-Finger Incidents
Last time, we discussed the first line of defense against fat finger incidents: limiting the number of BGP prefixes your router accepts from a BGP neighbor. However, you can do much more without deploying customer-specific filters (which might require a customer database) or ROV/RPKI.
You can practice the default filters you should always deploy on EBGP sessions with your customers in the Stop the Propagation of Configuration Errors lab exercise.
FRRouting RIB and FIB
This is how we described the interactions between routing protocol tables, RIB, and FIB in the ancient times:
- Routing protocols compute the best paths to all known prefixes.
- These paths compete for entry in the routing table. The path(s) with the lowest administrative distance win.
- The entries from the routing table are fully evaluated (in particular, their next hops) and entered in the forwarding table.
Let’s use a simple BGP+OSPF network to illustrate what I’m talking about:
FRRouting RIB and FIB
This is how we described the interactions between routing protocol tables, RIB, and FIB in the ancient times:
- Routing protocols compute the best paths to all known prefixes.
- These paths compete for entry in the routing table. The path(s) with the lowest administrative distance win.
- The entries from the routing table are fully evaluated (in particular, their next hops) and entered in the forwarding table.
Let’s use a simple BGP+OSPF network to illustrate what I’m talking about:
Interface EBGP Sessions on Arista EOS
Arista EOS and Cisco Nexus OS got interface EBGP sessions years after Cumulus Linux. While they’re trivially easy to configure on FRRouting (the routing daemon used by Cumulus Linux), getting them to work on Arista EOS is a bit tricky.
To make matters worse, my Google-Fu failed me when I tried to find a decent step-by-step configuration guide; all I got was a 12-minute video full of YouTube ads. Let’s fix that.
Interface EBGP Sessions on Arista EOS
Arista EOS and Cisco Nexus OS got interface EBGP sessions years after Cumulus Linux. While they’re trivially easy to configure on FRRouting (the routing daemon used by Cumulus Linux), getting them to work on Arista EOS is a bit tricky.
To make matters worse, my Google-Fu failed me when I tried to find a decent step-by-step configuration guide; all I got was a 12-minute video full of YouTube ads. Let’s fix that.