nanog mailing list archives
Re: maximum ipv4 bgp prefix length of /24 ?
From: William Herrin <bill () herrin us>
Date: Fri, 29 Sep 2023 16:36:47 -0700
On Fri, Sep 29, 2023 at 3:26 PM Owen DeLong <owen () delong com> wrote:
On Sep 29, 2023, at 15:14, William Herrin <bill () herrin us> wrote: I'm less assuming it and more reading it from this SIGCOMM paper: https://people.csail.mit.edu/ghobadi/papers/trio_sigcomm_2022.pdfFair enough, but interestingly, I think that the compiled line-card forwarding table probably always fits in the cache.
If I were designing the product, I'd size the SRAM with that in mind. I'd also keep two full copies of the FIB in the outer DRAM so that the PPEs could locklessly access the active one while the standby one gets updated with changes from the RIB. But I'd design the router to gracefully fail if the FIB exceeded what the SRAM could hold. When a TCAM fills, the shortest prefixes are ejected to the router's main CPU. That fails pretty hard since the shortest prefixes tend to be among the most commonly used. By comparison, an SRAM cache tends to retain the most commonly used prefixes as an inherent part of how caches work, regardless of prefix length. It can operate close to full speed until the actively used routes no longer fit in the cache. Regards, Bill Herrin -- William Herrin bill () herrin us https://bill.herrin.us/
Current thread:
- Re: maximum ipv4 bgp prefix length of /24 ?, (continued)
- Re: maximum ipv4 bgp prefix length of /24 ? William Herrin (Sep 29)
- Re: maximum ipv4 bgp prefix length of /24 ? Tom Beecher (Sep 29)
- Re: maximum ipv4 bgp prefix length of /24 ? William Herrin (Sep 29)
- Re: maximum ipv4 bgp prefix length of /24 ? Tom Beecher (Sep 29)
- RE: maximum ipv4 bgp prefix length of /24 ? Tony Wicks (Sep 29)
- Re: maximum ipv4 bgp prefix length of /24 ? William Herrin (Sep 29)
- Re: maximum ipv4 bgp prefix length of /24 ? Owen DeLong via NANOG (Sep 29)
- Re: maximum ipv4 bgp prefix length of /24 ? William Herrin (Sep 29)
- Re: maximum ipv4 bgp prefix length of /24 ? Tom Beecher (Sep 29)
- Re: maximum ipv4 bgp prefix length of /24 ? Owen DeLong via NANOG (Sep 29)
- Re: maximum ipv4 bgp prefix length of /24 ? William Herrin (Sep 29)
- Re: maximum ipv4 bgp prefix length of /24 ? Mark Tinka (Sep 30)
- Re: maximum ipv4 bgp prefix length of /24 ? Owen DeLong via NANOG (Sep 30)
- Re: maximum ipv4 bgp prefix length of /24 ? Owen DeLong via NANOG (Sep 29)
- Re: maximum ipv4 bgp prefix length of /24 ? Saku Ytti (Sep 29)
- Re: maximum ipv4 bgp prefix length of /24 ? VOLKAN SALİH (Sep 29)
- Re: maximum ipv4 bgp prefix length of /24 ? William Herrin (Sep 28)