tl;dr: comcast: does your 50.242.151.5 westin router receive the announcement of 147.28.0.0/20 from sprint's westin router 144.232.9.61? details: 3130 in the westin announces 147.28.0.0/19 and 147.28.0.0/20 to sprint, ntt, and the six and we want to remove the /19 when we stop announcing the /19, a traceroute to comcast through sprint dies at the handoff from sprint to comcast. r0.sea#traceroute 73.47.196.134 source 147.28.7.1 Type escape sequence to abort. Tracing the route to c-73-47-196-134.hsd1.ma.comcast.net (73.47.196.134) VRF info: (vrf in name/id, vrf out name/id) 1 r1.sea.rg.net (147.28.0.5) 0 msec 1 msec 0 msec 2 sl-mpe50-sea-ge-0-0-3-0.sprintlink.net (144.232.9.61) [AS 1239] 1 msec 1 msec 0 msec 3 * * * 4 * * * 5 * * * 6 * * * this would 'normally' (i.e. when the /19 is announced) be r0.sea#traceroute 73.47.196.134 source 147.28.7.1 Type escape sequence to abort. Tracing the route to c-73-47-196-134.hsd1.ma.comcast.net (73.47.196.134) VRF info: (vrf in name/id, vrf out name/id) 1 r1.sea.rg.net (147.28.0.5) 0 msec 1 msec 0 msec 2 sl-mpe50-sea-ge-0-0-3-0.sprintlink.net (144.232.9.61) [AS 1239] 1 msec 0 msec 1 msec 3 be-207-pe02.seattle.wa.ibone.comcast.net (50.242.151.5) [AS 7922] 1 msec 0 msec 0 msec 4 be-10847-cr01.seattle.wa.ibone.comcast.net (68.86.86.225) [AS 7922] 1 msec 1 msec 2 msec etc specifically, when 147.28.0.0/19 is announced, traceroute from 147.28.7.2 through sprint works to comcast. withdraw 147.28.0.0/19, leaving only 147.28.0.0/20, and the traceroute enters sprint but fails at the handoff to comcast. Bad next-hop? not propagated? covid? magic? which is why we wonder what comcast (50.242.151.5) hears from sprint at that handoff note that, at the minute, both the /19 and the /20 are being announced, as we want things to work. so you will not be able to reproduce. so, comcast, are you receiving the announcement of the /20 from sprint? with a good next-hop? randy