Transcript BGP Oscillation

Swinog-3, 19 September 2001
IP-Multicast operational experience
André Chapuis, IP-Plus
Swinog-3, Multicast operational experience
Network design
 Standard internet protocols
– PIM-SM
– MSDP
– MBGP
 Redundant RP with anycast-RP
 Recommended filters for MSDP/PIM
–
ftp://ftpeng.cisco.com/ipmulticast/config-notes/msdp-sa-filter.txt
 Customer’s RP filtered
–
Accept only SA-messages originated by specific RP’s
 Congruent IMBGP/IBGP topologies
 MBGP only where necessary
Swinog-3, Multicast operational experience
Network layout: MBGP
Swinog-3, Multicast operational experience
Network layout: MSDP
Swinog-3, Multicast operational experience
Observations/problems
 MBGP: RPF checks:
 IOS 12.0(7)T: MBGP used to leak into the unicast RIB !
 First trial abruptly stopped…
 Distance-preferred lookups, not longest-match !
 Problems with aggregates (network statements)
 Where to inject prefixes into MBGP if RPF checks
are done with network statements rather than IGP
route !
 Confed-external IMBGP were set a distance of 20 (bug)
 Occurred in IOS 12.0(10)S1 only
 Caused routing loops
 MBGP/BGP distance needs manual adaptation
Swinog-3, Multicast operational experience
Observations/problems
 MSDP: peer-RPF checks:
 How it works:
 When SA-message received, MSDP originator-id is
RPF checked with MBGP source AS (to avoid loops
when re-transmitting SA-messages)
 Issue:
 if ISP1 uses parallel MSDP/MBGP peerings and ISP2
only MSDP from its RP: RPF fails
 Seen with ‘debug ip msdp’ (use with care !)
 Use I-MSDP sessions or mesh-groups to bypass RPF
checks
Swinog-3, Multicast operational experience
Observations/problems
 MDS (Multicast Distributed Switching) bug(?) on IOS
12.0(16.6)S2, Cisco7513, VIP4-80, PA-H, Frame-relay p2p subinterfaces:
 MDS stops forwarding packets after some time (~1min)
 Turn off MDS
 Could only be seen with sh ip mroute 233.21.90.1 count
because all the routing tables and forwarding tables were
looking fine !
 Always check packet-forwarding (once the multicast
RT is OK)
Swinog-3, Multicast operational experience
Observations/problems
i64beb-eng#sh ip mrou 159.134.237.179 233.21.90.1 count
IP Multicast Statistics
207 routes using 72786 bytes of memory
28 groups, 6.39 average sources per group
Forwarding Counts: Pkt Count/Pkts per second/Avg Pkt Size/Kilobits per second
Other counts: Total/RPF failed/Other drops(OIF-null, rate-limit etc)
Group: 233.21.90.1, Source count: 51, Group pkt count: 234997
Source: 159.134.237.179/32, Forwarding: 226320/44/663/247, Other: 226320/0/0
Swinog-3, Multicast operational experience
Debugging
 mtrace <group> : uses RPF neighbors up to the source
 mtrace <source> <dest> <group>: follows SPT for the group
 mstat <source> <dest> <group>: gives packet-loss along the SPT
 show ip mroute <group> count: gives actually forwarded packets
 http://www.on-the-i.com/mt/index.html: tests from your host !
Swinog-3, Multicast operational experience
Mtrace example

i64beb-eng#mtrace 159.134.237.179 195.65.89.1 233.20.90.1

Type escape sequence to abort.

Mtrace from 159.134.237.179 to 195.65.89.1 via group 233.20.90.1

From source (dipsy.av.eircom.net) to destination (i64beb-eng-FastEthernet0-0.ip-plus.net)

Querying full reverse path...

0 i64beb-eng-FastEthernet0-0.ip-plus.net (195.65.89.1)

-1 i64beb-eng-FastEthernet0-0.ip-plus.net (195.65.89.1) PIM [default]

-2 i64beb-021-atm4-0.ip-plus.net (164.128.156.249) PIM/MBGP [159.134.0.0/16]

-3 i62beb-031-fas-2-0.ip-plus.net (164.128.129.230) PIM [159.134.0.0/16]

-4 i64bei-000-Hssi1-0-5.ip-plus.net (164.128.49.13) PIM/MBGP [159.134.0.0/16]

-5 ges-005-Serial3-1.ip-plus.net (164.128.33.129) PIM/MBGP [159.134.0.0/16]

-6 lon-000-Serial2-0.ip-plus.net (164.128.34.14) PIM/MBGP [159.134.0.0/16]

-7 lon-005-POS2-0.ip-plus.net (164.128.33.14) PIM/MBGP [159.134.0.0/16]

-8 fa0.mcast1.thn.london.eircom.net (195.66.230.20) PIM [159.134.237.176/29]

-9 fa5-0-0.core1.thn.london.eircom.net (159.134.191.49) PIM [159.134.237.176/29]

-10 pos1-0-0.core1.cra.dublin.eircom.net (159.134.191.97) PIM [159.134.237.176/29]

-11 e0.mbone.cra.dublin.eircom.net (159.134.192.55) PIM [159.134.237.176/29]

-12 dipsy.av.eircom.net (159.134.237.179)
Swinog-3, Multicast operational experience
Facts
 Global MBGP table contains 3751 entries
 IP-Plus currently has 15 multicast peerings
 Some popular Websites offer multicast contents:
– www.on-the-i.com
– www.broadcast.com (Yahoo, through AS3356 (Level3)
– From last week on, Mbone session:
– UO internal channel 2 sends CNN live