Dell PowerSwitch S4820T Configuration Guide for the S4820T System 9.100.0 - Page 173

Configuration Information, BGP Configuration, Information

Page 173 highlights

• High CPU utilization may be observed during an SNMP walk of a large BGP Loc-RIB. • To avoid SNMP timeouts with a large-scale configuration (large number of BGP neighbors and a large BGP Loc-RIB), Dell Networking recommends setting the timeout and retry count values to a relatively higher number. For example, t = 60 or r = 5. • To return all values on an snmpwalk for the f10BgpM2Peer sub-OID, use the -C c option, such as snmpwalk -v 2c -C c -c public. • An SNMP walk may terminate pre-maturely if the index does not increment lexicographically. Dell Networking recommends using options to ignore such errors. • Multiple BPG process instances are not supported. Thus, the f10BgpM2PeerInstance field in various tables is not used to locate a peer. • Multiple instances of the same NLRI in the BGP RIB are not supported and are set to zero in the SNMP query response. • The f10BgpM2NlriIndex and f10BgpM2AdjRibsOutIndex fields are not used. • Carrying MPLS labels in BGP is not supported. The f10BgpM2NlriOpaqueType and f10BgpM2NlriOpaquePointer fields are set to zero. • 4-byte ASN is supported. The f10BgpM2AsPath4byteEntry table contains 4-byte ASN-related parameters based on the configuration. • If a received update route matches with a local prefix, then that route is discarded. This behavior results from an incorrect BGP configuration. To overcome this issue, you can trigger a route refresh after you properly configure BGP. Traps (notifications) specified in the BGP4 MIB draft are not supported. Such traps (bgpM2Established and bgpM2BackwardTransition) are supported as part of RFC 1657. Configuration Information The software supports BGPv4 as well as the following: • deterministic multi-exit discriminator (MED) (default) • a path with a missing MED is treated as worst path and assigned an MED value of (0xffffffff) • the community format follows RFC 1998 • delayed configuration (the software at system boot reads the entire configuration file prior to sending messages to start BGP peer sessions) The following are not yet supported: • auto-summarization (the default is no auto-summary) • synchronization (the default is no synchronization) BGP Configuration To enable the BGP process and begin exchanging information, assign an AS number and use commands in ROUTER BGP mode to configure a BGP neighbor. By default, BGP is disabled. By default, Dell Networking OS compares the MED attribute on different paths from within the same AS (the bgp always-comparemed command is not enabled). NOTE: In Dell Networking OS, all newly configured neighbors and peer groups are disabled. To enable a neighbor or peer group, enter the neighbor {ip-address | peer-group-name} no shutdown command. The following table displays the default values for BGP on Dell Networking OS. Table 9. BGP Default Values Item BGP Neighbor Adjacency changes Fast External Fallover feature Graceful Restart feature Default All BGP neighbor changes are logged. Disabled Disabled Border Gateway Protocol IPv4 (BGPv4) 173

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High CPU utilization may be observed during an SNMP walk of a large BGP Loc-RIB.
To avoid SNMP timeouts with a large-scale
configuration
(large number of BGP neighbors and a large BGP Loc-RIB), Dell Networking
recommends setting the timeout and retry count values to a relatively higher number. For example, t = 60 or r = 5.
To return all values on an snmpwalk for the
f10BgpM2Peer sub-OID
, use the
-C c
option, such as
snmpwalk -v 2c -C c -c
public<IP_address><OID>
.
An SNMP walk may terminate pre-maturely if the index does not increment lexicographically. Dell Networking recommends using
options to ignore such errors.
Multiple BPG process instances are not supported. Thus, the
f10BgpM2PeerInstance
field
in various tables is not used to locate a peer.
Multiple instances of the same NLRI in the BGP RIB are not supported and are set to zero in the SNMP query response.
The
f10BgpM2NlriIndex
and
f10BgpM2AdjRibsOutIndex
fields
are not used.
Carrying MPLS labels in BGP is not supported. The
f10BgpM2NlriOpaqueType
and
f10BgpM2NlriOpaquePointer
fields
are set to zero.
4-byte ASN is supported. The
f10BgpM2AsPath4byteEntry
table contains 4-byte ASN-related parameters based on the
configuration.
If a received update route matches with a local
prefix,
then that route is discarded. This behavior results from an incorrect BGP
configuration.
To overcome this issue, you can trigger a route refresh after you properly
configure
BGP.
Traps
(notifications)
specified
in the BGP4 MIB draft
<draft-ietf-idr-bgp4–mibv2–05.txt>
are not supported. Such traps
(
bgpM2Established
and
bgpM2BackwardTransition
) are supported as part of RFC 1657.
Configuration
Information
The software supports BGPv4 as well as the following:
deterministic multi-exit discriminator (MED) (default)
a path with a missing MED is treated as worst path and assigned an MED value of
(0xffffffff)
the community format follows RFC 1998
delayed
configuration
(the software at system boot reads the entire
configuration
file
prior to sending messages to start BGP peer
sessions)
The following are not yet supported:
auto-summarization (the default is no auto-summary)
synchronization (the default is no synchronization)
BGP
Configuration
To enable the BGP process and begin exchanging information, assign an AS number and use commands in ROUTER BGP mode to
configure
a BGP neighbor.
By default, BGP is disabled.
By default, Dell Networking OS compares the MED attribute on
different
paths from within the same AS (the
bgp always-compare-
med
command is not enabled).
NOTE:
In Dell Networking OS, all newly
configured
neighbors and peer groups are disabled. To enable a neighbor or peer group,
enter the
neighbor {
ip-address
|
peer-group-name
} no shutdown
command.
The following table displays the default values for BGP on Dell Networking OS.
Table 9. BGP Default Values
Item
Default
BGP Neighbor Adjacency changes
All BGP neighbor changes are logged.
Fast External Fallover feature
Disabled
Graceful Restart feature
Disabled
Border Gateway Protocol IPv4 (BGPv4)
173