In non-deterministic mode (the
bgp non-deterministic-med
command is applied), paths are compared in the order in which they
arrive. This method can lead to Dell Networking OS choosing different best paths from a set of paths, depending on the order in which they
were received from the neighbors because MED may or may not get compared between the adjacent paths. In deterministic mode, Dell
Networking OS compares MED between the adjacent paths within an AS group because all paths in the AS group are from the same AS.
NOTE:
The
bgp bestpath as-path multipath-relax
command is disabled by default, preventing BGP from load-
balancing a learned route across two or more eBGP peers. To enable load-balancing across different eBGP peers, enable the
bgp
bestpath as-path multipath-relax
command. A system error results if you configure the
bgp bestpath as-path
ignore
command and the
bgp bestpath as-path multipath-relax
command at the same time. Only enable one
command at a time.
The following illustration shows that the decisions BGP goes through to select the best path. The list following the illustration details the
path selection criteria.
Figure 20. BGP Best Path Selection
Best Path Selection Details
1
Prefer the path with the largest WEIGHT attribute.
2
Prefer the path with the largest LOCAL_PREF attribute.
3
Prefer the path that was locally
Originated via a network
command,
redistribute
command or
aggregate-address
command.
a
Routes originated with the
Originated via a network
or
redistribute
commands are preferred over routes
originated with the
aggregate-address
command.
4
Prefer the path with the shortest AS_PATH (unless the
bgp bestpath as-path ignore
command is configured, then
AS_PATH is not considered). The following criteria apply:
a
An AS_SET has a path length of 1, no matter how many ASs are in the set.
b
A path with no AS_PATH configured has a path length of 0.
c
AS_CONFED_SET is not included in the AS_PATH length.
d
AS_CONFED_SEQUENCE has a path length of 1, no matter how many ASs are in the AS_CONFED_SEQUENCE.
5
Prefer the path with the lowest ORIGIN type (IGP is lower than EGP, and EGP is lower than INCOMPLETE).
6
Prefer the path with the lowest multi-exit discriminator (MED) attribute. The following criteria apply:
a
This comparison is only done if the first (neighboring) AS is the same in the two paths; the MEDs are compared only if the first
AS in the AS_SEQUENCE is the same for both paths.
b
If you entered the
bgp always-compare-med
command, MEDs are compared for all paths.
c
Paths with no MED are treated as “worst” and assigned a MED of 4294967295.
Border Gateway Protocol IPv4 (BGPv4)
181
Содержание S4048T-ON
Страница 1: ...Dell Configuration Guide for the S4048 ON System 9 11 2 1 ...
Страница 148: ...Figure 10 BFD Three Way Handshake State Changes 148 Bidirectional Forwarding Detection BFD ...
Страница 251: ...Dell Control Plane Policing CoPP 251 ...
Страница 363: ... RPM Synchronization GARP VLAN Registration Protocol GVRP 363 ...
Страница 511: ...Figure 64 Inspecting the LAG Configuration Link Aggregation Control Protocol LACP 511 ...
Страница 512: ...Figure 65 Inspecting Configuration of LAG 10 on ALPHA 512 Link Aggregation Control Protocol LACP ...
Страница 515: ...Figure 67 Inspecting a LAG Port on BRAVO Using the show interface Command Link Aggregation Control Protocol LACP 515 ...
Страница 516: ...Figure 68 Inspecting LAG 10 Using the show interfaces port channel Command 516 Link Aggregation Control Protocol LACP ...
Страница 558: ...Figure 84 Configuring Interfaces for MSDP 558 Multicast Source Discovery Protocol MSDP ...
Страница 559: ...Figure 85 Configuring OSPF and BGP for MSDP Multicast Source Discovery Protocol MSDP 559 ...
Страница 560: ...Figure 86 Configuring PIM in Multiple Routing Domains 560 Multicast Source Discovery Protocol MSDP ...
Страница 564: ...Figure 88 MSDP Default Peer Scenario 2 564 Multicast Source Discovery Protocol MSDP ...
Страница 565: ...Figure 89 MSDP Default Peer Scenario 3 Multicast Source Discovery Protocol MSDP 565 ...
Страница 729: ...protocol spanning tree pvst no disable vlan 300 bridge priority 4096 Per VLAN Spanning Tree Plus PVST 729 ...
Страница 841: ...Figure 115 Single and Double Tag TPID Match Service Provider Bridging 841 ...
Страница 842: ...Figure 116 Single and Double Tag First byte TPID Match 842 Service Provider Bridging ...