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INCIDENT REPLAY · 2021-02-13

Cablevision Mexico (AS28548) leaks about 7,200 prefixes

For about 12 minutes from 04:36 UTC an AS that normally announces about 150 routes announced over 7,200 IPv4 prefixes, many of them more-specifics, through one of its upstreams.

Mis-originationOptimizer more specificsCatalog confidence: medium

A reconstruction, not the operator's network. Hammerhead's authors rebuilt the change from the public record as a small network of their own. No configuration here is the operator's. What follows is what the tool reported on that reconstruction; it is not a claim that the tool would have prevented the outage.

What happened

Who: Cablevision S.A. de C.V. (AS28548) caused; leaked via AS18734; more than 1,290 ASes in over 100 countries touched

The summary at the top is paraphrased from the sources below. Hammerhead's catalog rates its confidence in this account medium.

Sources

What the public record says

  • For about 12 minutes from 04:36 UTC an AS that normally announces about 150 routes announced over 7,200 IPv4 prefixes, many of them more-specifics, through one of its upstreams.
  • Who: Cablevision S.A. de C.V. (AS28548) caused; leaked via AS18734; more than 1,290 ASes in over 100 countries touched

What the reconstruction assumed

Decided by Hammerhead's authors to build a network that runs. None of it describes the operator's network.

Everything below is ours.

  • The family template (tools/replays/gen_family_misorigination.py): CABLEVISION-1 (AS 28548), an upstream UP-1 (AS 18734) that prefers its customer's routes and filters nothing on that session, the victim, and a third party behind the upstream. CABLEVISION-1 forwards the traffic it draws on to the victim over a second link.
  • Cisco IOS syntax. No operator here has published configuration, and which vendors they ran is not on the record.
  • The upstream's other sessions are filtered and limited, so that the audit's finding is about this session and not the template.
  • CABLEVISION-1 exports with the ordinary customer policy, an AS-path filter that passes only what it originates (^$). A mis-originated prefix is locally originated, so it passes.
  • Stand-in address space; about 7,200 prefixes in the event.

What Hammerhead said

Each run below is pinned by Hammerhead's replay tests at commit 0ee9732: the verdict and the quoted text are checked against the tool's output, and a run that disagrees fails the test. Reason lines are copied verbatim; a pinned line can be part of a longer reason. Every preflight run uses --max-blast-radius 100, so a change is never counted as caught merely because it touched many devices of a small network.

every network in one snapshot

now: fail

On the reconstruction, hammerhead preflight on a before and an after snapshot returned fail, for the reasons below.

Reason text pinned (some reason contains each line)

  • CABLEVISION-1 would start originating 198.18.0.0/21, which is inside 198.18.0.0/20 that it learns from
  • path change:

First run, before the fixes this batch prompted

first: fail
  • external advertisements: CABLEVISION-1 would start originating 198.18.0.0/21, which is inside 198.18.0.0/20 that it learns from AS 64510. A more-specific of address space you receive from a peer is not yours to announce
  • external advertisements: CABLEVISION-1 would start originating 198.18.8.0/21, which is inside 198.18.0.0/20 that it learns from AS 64510. A more-specific of address space you receive from a peer is not yours to announce

Pinned in tests/gauntlet/replays-misorigination.yaml.

CABLEVISION-1's own router, nothing declared: a new origination is reported, and only a caveat

now: pass

On the reconstruction, hammerhead preflight on a before and an after snapshot returned pass.

Caveats pinned (some caveat contains each line; a caveat never moves the verdict)

  • CABLEVISION-1 would start announcing 2 prefix(es) to

First run, before the fixes this batch prompted

first: unknown

Pinned in tests/gauntlet/replays-misorigination.yaml.

CABLEVISION-1's own router, with what the upstream sends declared

now: fail

On the reconstruction, hammerhead preflight on a before and an after snapshot with --boundary @cablevision_2021/boundary.yaml returned fail, for the reasons below.

Reason text pinned (some reason contains each line)

  • CABLEVISION-1 would start announcing 198.18.0.0/21 to
  • which is inside 198.18.0.0/20 that
  • (AS 18734) advertises to this network (declared by

First run, before the fixes this batch prompted

first: fail
  • external advertisements: CABLEVISION-1 would start announcing 198.18.0.0/21 to 172.16.1.1 (AS 18734), which is inside 198.18.0.0/20 that 172.16.1.1 (AS 18734) advertises to this network (declared by noc@example.net). A more-specific of address space you receive from a peer is not yours to announce
  • external advertisements: CABLEVISION-1 would start announcing 198.18.8.0/21 to 172.16.1.1 (AS 18734), which is inside 198.18.0.0/20 that 172.16.1.1 (AS 18734) advertises to this network (declared by noc@example.net). A more-specific of address space you receive from a peer is not yours to announce
  • external advertisements: CABLEVISION-1 would start announcing 198.18.0.0/21 to 172.16.3.2 (AS 64510), which is inside 198.18.0.0/20 that 172.16.1.1 (AS 18734) advertises to this network (declared by noc@example.net). A more-specific of address space you receive from a peer is not yours to announce
  • external advertisements: CABLEVISION-1 would start announcing 198.18.8.0/21 to 172.16.3.2 (AS 64510), which is inside 198.18.0.0/20 that 172.16.1.1 (AS 18734) advertises to this network (declared by noc@example.net). A more-specific of address space you receive from a peer is not yours to announce

Pinned in tests/gauntlet/replays-misorigination.yaml.

UP-1's own router, no change: the audit

now: fail (finding)

An audit of one snapshot, no change: hammerhead nqe-library --mode run, check nqe.bgp.ebgp_peer_unfiltered_and_unlimited. Pinned status: fail, a finding whose evidence contains the text below.

Evidence pinned (the evidence contains each line)

  • UP-1
  • 28548

First run, before the fixes this batch prompted

first: pass (no finding)

Pinned in tests/gauntlet/replays-misorigination.yaml.

every network in one snapshot (potential microloop)

now: fail

On the reconstruction, hammerhead preflight on a before and an after snapshot returned fail.

This run repeats another pinned run (same snapshots, flags and verdict) to record the potential microloops it finds. A caveat never moves the verdict.

Caveats pinned (some caveat contains each line; a caveat never moves the verdict)

  • INET-1 -> UP-1 -> INET-1, if INET-1 has its new next hop while UP-1 still has its old one

Pinned in tests/gauntlet/replays-transients.yaml.

What changed in Hammerhead because of it

From the “What was fixed” table in Hammerhead's replay notes, where each fix landed after a failing test. “Found by” is copied as written; a family name means the batch this incident belongs to.

ROA maximum length

Roa::covers_prefix refused to cover a more-specific beyond maxLength, so such a prefix came back NotFound instead of Invalid (RFC 6811).

Found by: Mis-origination family

--roas <FILE> origin-validates new originations

From the originator's own seat a block that escapes is one new prefix, and only a caveat. With a validator's export it is decidable: "the ROA for 104.244.42.0/24 authorises AS 13414".

Found by: Mis-origination family

An announcement that multiplies

The announcement to an external peer goes from a few prefixes to many in one change.

Found by: Mis-origination family, Level 3

Outbound policy runs before the local AS is prepended

The simulator prepended first, so an outbound filter-list with ^$ matched nothing the router originated.

Found by: Mis-origination family

Many foreign originations are one reason

A mass mis-origination of hundreds of prefixes was hundreds of reasons.

Found by: Mis-origination family

Limits

  • The configurations are a reconstruction. Where the record is silent, the assumptions above fill the gap; if one is wrong, the replay is wrong in that respect.
  • A verdict describes the reconstructed network's converged state. Timing, traffic load, and anything a device does that no configuration states, such as software reacting to a health check or a firmware bug, are outside it.
  • A pass is reported as a pass. A fail says a gate fired on the reconstruction, nothing more.
  • Why the catalog counts this outage as in scope: Optimizer output with an export path, and an upstream customer session with no max-prefix able to trip at 50 times the normal count.

Not fixed: A single-prefix hijack from the hijacker's own seat, with no ROA and nothing declared

One new origination is what a legitimate new prefix looks like. pass with the caveat naming it; --roas or --boundary decides it.

Recorded against: Mis-origination family (17 of 28)

Not fixed: A forged-origin hijack

Origin validation passes it by construction. ASPA is not modelled.

Recorded against: Mis-origination family

Imported from docs/replays/cablevision-2021/FACTS.md and the replay manifests in the Hammerhead repository at commit 0ee9732.