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What will happen when the routing table hits 1024k

  • Posted at 2022-11-08 22:46:42
  • By Prefixx Team

What will happen when the routing table hits 1024k

An exciting and important milestone occurred in the history of the internet on 12th August 2014. The IPv4 routing table limit crossed 512,000 border gateway protocol (BGP) routes. Many network operators were using older kits and were not prepared. They landed in trouble.


The event led to a FIB or Forwarding Information Base limit of 512k on common routers. Over the years, both IPv4 and IPv6 prefixes have been increasing. While IPv4 is growing at 6%, IPv6 is growing at 33%.


As of January 2021, the number of routes was 861,418 for IPv4 and 109,398 for IPv6. The question arises as to what is the next limit that may lead to a 2014-like event occurring. Most importantly, when the limit is breached what would happen?


The key numbers to know


Every router is set with a maximum size for the routing table. It is believed that many of the routers have their IPv4 limit at 1024k, which is 1,048,576 routes. For IPv6, the number is 128k or 131,072 routes.

Keeping in mind the present trends, it is expected that the IPv4 limit of 1024k is likely to be breached by the end of 2023. Based on current trends, the 128k IPv6 milestone is likely to be around the end of 2022.


Before we get into the issue of what happens when the number is breached, it is essential to note that not all operators are the same. Various factors could affect the internal tables of operators. The factors include:


· The topology, which could be MPLS or Native IP.

· The ISIS/OSPF size of the Internet Gateway Protocol (IGP).

· The BGP families labeled unicast, and

· Customer routes


What are the likely scenarios?


It is now time to look at and understand what would happen when the 1024k limit is breached for IPv4. There are various scenarios that could occur:


· It is possible that there is a routing table leak of anywhere from 10k to 30k. A similar leak of 22k occurred during the 2014 event. If such a leak occurs, the limit could be breached earlier.

· If many operators are affected when the limit is breached, it could then lead to a significant situation.

· There could be an impact on operator networks, and this depends on the network deployment.

· It is also possible that the operator optimizes their network before time, and hence nothing of significance occurs.

There are two checks that the latest operators can perform on the limits of their network devices. One is to check the hardware and silicon architecture limit on all the different models of routers. The second is to check the standards and configuration for the network operating system.


Checking the hardware


If all the network operators would use the latest hardware, then there would not be a problem. This is because the hardware has higher route limits. But the problem is that because of practical issues, many operators are using older hardware. Since there are different routers used, this could be an issue.


The key here is for network operators to buy routers that can handle all three tables. These include the BGP RIB (Border Gateway Protocol Routing Information Base), FIB (Forwarding Information Base), and RIB (Routing Information Base). These are the tables where the IP address prefixes are stored.


Newer routers can handle these tables allowing even to manage future needs. The operator should be able to anticipate future scale needs for their router deployment and use cases.


If it is impossible to change the routers, then the operator must optimize the RIB and FIB use. The TCAM size can be adjusted, and control routes can be adjusted from RIB to FIB. This can be done in consultation with the router manufacturers to be prepared.


Network OS configurations


The configuration standards for the network operating system need to be reviewed. It is required that the operators review their iBGP configurations. The maximum prefix for the OS may need to be adjusted. This would help avoid resetting iBGP sessions and subsequent issues.

Operators should thus prepare themselves by properly reviewing the hardware and software scale limits. They also need to check the FIB and RIB limits. Finally, they can get in touch with the router vendor to validate the route optimization knobs in line with the network environment.

The operators, network admins, and builders must optimize their network. This will ensure a reliable, secure, and stable internet. They need to use an iterative and continuous approach to make this happen.

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