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Would call it stretch to say it was widely used by ISPs. Some old ones may still be using integrated IS-IS as their IGP (early OSPF had scaling issues and compl

Would call it stretch to say it was widely used by ISPs. Some old ones may still be using integrated IS-IS as their IGP (early OSPF had scaling issues and complicated solutions for that), but that's nothing like widely using the ISO stack. But they might have used IS-IS it to route NSAP in their network at some point in time to manage ATM-era equipment, the ISP I worked still had some ctunnels for that purpose, I doubt they still have them.

p_l 2y ago
It was still widely used for IPv4 and v6 in 2000s. ex telco engineer told us that two major reasons was that IS-IS was simply more efficient, and that they didn't require IP communication between routers - meaning troubleshooting and management was easier than providing p2p routes for IP-based protocols.
- Hikikomori 2y ago
  It's still widely used, among old ISPs because why switch when it's just as good or better than the alternative and your engineers know it best. But it's not the whole stack as implied in the first reply. It was popular primarily because OSPF didn't scale well with hundreds to thousands of routers with the minimal CPU power even large core routers had.
  - p_l 2y ago
    Scalability was one part. Later the fact that you didn't need separate routing setup for v6 also was part of it. But for a telco, the fact that you didn't have to setup IP connectivity in order for routers to see each other, was also a crucial ability.
    - Hikikomori 2y ago
      OSPF has supported unnumbered links for a long time, don't need IP on the link with point to point and multicast.
      - p_l 2y ago
        Unnumbered just means you have no IP address exclusive to the link. IS-IS works without establishing IP connectivity at all, not just about tricks to handle leaky internals. This also meant autoconfiguration or supporting non-ip protocols (like routed ethernet) is simpler, though I will admit that OSPFv3 adding default use of link local V6 for router interfaces made the gap smaller.
yusyusyus 2y ago
still good reasons to choose IS-IS for greenfield :) hell, they took IS-IS and did TRILL with it for DC (rip TRILL). but yeah, I saw one piece of SONET crap hanging off a ctunnel that spoke CLNP back in maybe 2012 or 2013? haven't seen much of it, but still learned the ctunnel stuff back in '09 because it still could occasionally rear its head.
- Hikikomori 2y ago
  Worked for an old ISP in 2012 (it started when the state owned telco was privatized). Also had the ctunnel to manage old SONET crap, still had modem pools running, racks full of purple Sun machines still running, vax, hpux, as400, etc. Even the old smsc that was 5 racks of dec servers was still there, was never removed as they didn't need the space because modern equipment was using all the available power anyway (was also in a mountain so a bit of a hassle to remove).

p_l 2y ago

It was still widely used for IPv4 and v6 in 2000s. ex telco engineer told us that two major reasons was that IS-IS was simply more efficient, and that they didn't require IP communication between routers - meaning troubleshooting and management was easier than providing p2p routes for IP-based protocols.

Hikikomori 2y ago
It's still widely used, among old ISPs because why switch when it's just as good or better than the alternative and your engineers know it best. But it's not the whole stack as implied in the first reply. It was popular primarily because OSPF didn't scale well with hundreds to thousands of routers with the minimal CPU power even large core routers had.
- p_l 2y ago
  Scalability was one part. Later the fact that you didn't need separate routing setup for v6 also was part of it. But for a telco, the fact that you didn't have to setup IP connectivity in order for routers to see each other, was also a crucial ability.
  - Hikikomori 2y ago
    OSPF has supported unnumbered links for a long time, don't need IP on the link with point to point and multicast.
    - p_l 2y ago
      Unnumbered just means you have no IP address exclusive to the link. IS-IS works without establishing IP connectivity at all, not just about tricks to handle leaky internals. This also meant autoconfiguration or supporting non-ip protocols (like routed ethernet) is simpler, though I will admit that OSPFv3 adding default use of link local V6 for router interfaces made the gap smaller.

yusyusyus 2y ago

still good reasons to choose IS-IS for greenfield :) hell, they took IS-IS and did TRILL with it for DC (rip TRILL). but yeah, I saw one piece of SONET crap hanging off a ctunnel that spoke CLNP back in maybe 2012 or 2013? haven't seen much of it, but still learned the ctunnel stuff back in '09 because it still could occasionally rear its head.

Hikikomori 2y ago
Worked for an old ISP in 2012 (it started when the state owned telco was privatized). Also had the ctunnel to manage old SONET crap, still had modem pools running, racks full of purple Sun machines still running, vax, hpux, as400, etc. Even the old smsc that was 5 racks of dec servers was still there, was never removed as they didn't need the space because modern equipment was using all the available power anyway (was also in a mountain so a bit of a hassle to remove).