5 ms·

What causes the restriction of /24, rather than being able to route individual addresses?

casylum 4y ago
Routing tables need to be limited in size in order for hardware to decide where to route packets fast enough. In the past hardware was more cpu and memory bound than the present.
- Dylan16807 4y ago
  But also at present, dealing with millions of routes at the packet-switching level gets difficult. Especially because the speed of links has increased so much.
ikiris 4y ago
Physics. Routers can only handle so many routes, so their operators set floor values for size of route they'll generally accept.
- netr0ute 4y ago
  Then it's time for operators to get with the times, because routers today don't have those same limitations as before.
  - betaby 4y ago
    Nothing to do with with operators. Again, physics, notably tcam https://en.wikipedia.org/wiki/Content-addressable_memory#Ternary_CAMs https://en.wikipedia.org/wiki/Content-addressable_memory#Ter... very expensive.
  - wmf 4y ago
    Recent routers can handle 1M routes while the Internet routing table currently has... 928K routes. Allowing people to disaggregate further would blow out routers. I'm not counting gold-plated routers because I see no reason to force ISPs to buy those.
  - msbarnett 4y ago
    Do you have any conception of how much TCAM would be required to individually route 14 billion IP addresses? And even beyond that what else would be involved to route things fast enough at that granularity. A top end router today can handle ~million routes. You’re talking a four orders of magnitude increase.
    - netr0ute 4y ago
      Who said the prefixes had to go to /32? Just to /28 would only need 16 million routes.
      - lostapathy 4y ago
        Practical reasons of replacing "all the routers" aside ... would this even be desirable? Do we really want IP space carved up into smaller and smaller bites? Do we really want even more and smaller entities advertising routes into BGP? The big players have enough troubles with it - we don't need small businesses with a /28 playing in those waters.
        toast0 4y ago
        Kind of / maybe. At my last job, we wanted to host our own anycast nameservers. You get the best results from having four nameservers in DNS, and you want them independent, so there's four /24s out there doing not much other than DNS (I think there may be some other stuff now). On the other hand, some other changes meant our thousands of servers no longer had their own ipv4 addresses, so there's several /24s returned to the hosting provider to be used by others. There's a lot of value in owning your user-facing IPs and being able to move them around as needed, but a lot of services don't really have that many user facing IPs, so utilization is low if they get a /24 per location.
        lostapathy 4y ago
        I tend to think the amount of companies who want to do that AND could do it well is vanishingly low. On the converse - I think of all the smaller businesses I worked around that really wanted to get their own portable IP block and ASN because they thought it made them serious ... but just had no business playing in that space.
  - jleahy 4y ago
    TCAMs as shown in that page haven’t been used for a very very long time. Even in basic switches now the solution is ‘algorithmic TCAM’ (ie. something like hashtables or tries). Huge numbers of routes are simply not an issue these days, unless you have truly ancient crappy equipment (maybe it was second hand for example).
    - fomine3 4y ago
      It seems that Cisco distinguishes TCAM and Hash at least. https://quickview.cloudapps.cisco.com/quickview/bug/CSCvg60292 https://quickview.cloudapps.cisco.com/quickview/bug/CSCvg602... https://www.cisco.com/c/en/us/support/docs/switches/catalyst-9500-series-switches/217703-understand-hardware-resources-on-catalys.html https://www.cisco.com/c/en/us/support/docs/switches/catalyst...
      - jleahy 4y ago
        The documentation there is wrong/misleading.
  - zokier 4y ago
    Getting with the times these days means adopting ipv6, not putting more bandaids to ipv4

Routing tables need to be limited in size in order for hardware to decide where to route packets fast enough. In the past hardware was more cpu and memory bound than the present.

Dylan16807 4y ago
But also at present, dealing with millions of routes at the packet-switching level gets difficult. Especially because the speed of links has increased so much.

ikiris 4y ago

Physics. Routers can only handle so many routes, so their operators set floor values for size of route they'll generally accept.

netr0ute 4y ago
Then it's time for operators to get with the times, because routers today don't have those same limitations as before.
- betaby 4y ago
  Nothing to do with with operators. Again, physics, notably tcam https://en.wikipedia.org/wiki/Content-addressable_memory#Ternary_CAMs https://en.wikipedia.org/wiki/Content-addressable_memory#Ter... very expensive.
- wmf 4y ago
  Recent routers can handle 1M routes while the Internet routing table currently has... 928K routes. Allowing people to disaggregate further would blow out routers. I'm not counting gold-plated routers because I see no reason to force ISPs to buy those.
- msbarnett 4y ago
  Do you have any conception of how much TCAM would be required to individually route 14 billion IP addresses? And even beyond that what else would be involved to route things fast enough at that granularity. A top end router today can handle ~million routes. You’re talking a four orders of magnitude increase.
  - netr0ute 4y ago
    Who said the prefixes had to go to /32? Just to /28 would only need 16 million routes.
    - lostapathy 4y ago
      Practical reasons of replacing "all the routers" aside ... would this even be desirable? Do we really want IP space carved up into smaller and smaller bites? Do we really want even more and smaller entities advertising routes into BGP? The big players have enough troubles with it - we don't need small businesses with a /28 playing in those waters.
      - toast0 4y ago
        Kind of / maybe. At my last job, we wanted to host our own anycast nameservers. You get the best results from having four nameservers in DNS, and you want them independent, so there's four /24s out there doing not much other than DNS (I think there may be some other stuff now). On the other hand, some other changes meant our thousands of servers no longer had their own ipv4 addresses, so there's several /24s returned to the hosting provider to be used by others. There's a lot of value in owning your user-facing IPs and being able to move them around as needed, but a lot of services don't really have that many user facing IPs, so utilization is low if they get a /24 per location.
        lostapathy 4y ago
        I tend to think the amount of companies who want to do that AND could do it well is vanishingly low. On the converse - I think of all the smaller businesses I worked around that really wanted to get their own portable IP block and ASN because they thought it made them serious ... but just had no business playing in that space.
- jleahy 4y ago
  TCAMs as shown in that page haven’t been used for a very very long time. Even in basic switches now the solution is ‘algorithmic TCAM’ (ie. something like hashtables or tries). Huge numbers of routes are simply not an issue these days, unless you have truly ancient crappy equipment (maybe it was second hand for example).
  - fomine3 4y ago
    It seems that Cisco distinguishes TCAM and Hash at least. https://quickview.cloudapps.cisco.com/quickview/bug/CSCvg60292 https://quickview.cloudapps.cisco.com/quickview/bug/CSCvg602... https://www.cisco.com/c/en/us/support/docs/switches/catalyst-9500-series-switches/217703-understand-hardware-resources-on-catalys.html https://www.cisco.com/c/en/us/support/docs/switches/catalyst...
    - jleahy 4y ago
      The documentation there is wrong/misleading.
- zokier 4y ago
  Getting with the times these days means adopting ipv6, not putting more bandaids to ipv4