Routing Configuration Guide for vEdge Routers, Cisco SD-WAN Release 20.x

By default ,OMP is enabled on all Cisco vedge devices andCisco vSmart Controllers. OMP must be operational for Cisco SD-WAN overlay network to function. If you disable it, you disable the overlay network.

OMP support in Cisco SD-WAN includes the following:

• IPv4 andIPv6 protocols, which are both turned on by default for VPN 0

• OMP route advertisement to BGP , EIGRP , OSPF , connect route , static route , andso on

Configure OMP Graceful Restart

OMP graceful restart is enabled by default on Cisco vSmart Controllers andCisco SD-WAN device . OMP graceful restart is has has a timer that tell the OMP peer how long to retain the cached advertised route . When this
timer expire , the cached route are consider to be no long valid , andthe OMP peer flush them from its route table .

The default timer is 43,200 seconds (12 hours), andthe timer range is 1 through 604,800 seconds (7 days). To modify the default
timer value:

 device(config - omp ) # timer graceful - restart - timer second

To disable OMP graceful restart :

device(config-omp)# no omp graceful-restart

The graceful restart timer is set up independently on each OMP peer; that is, it’s set up separately on each Cisco vEdge device andCisco vSmart Controller. To illustrate what this means, let’s consider a vSmart controller that uses a graceful restart time of 300 seconds, or 5
minutes, anda Cisco vEdge device that is configured with a timer of 600 seconds (10 minutes). Here, Cisco vSmart Controller retains the OMP routes learned from that device for 10 minutes—the graceful restart timer value that is configured on the
device andthat the device has sent to Cisco vSmart Controller during the setup of the OMP session. The Cisco vEdge device retain the route it learn from the vSmart controller for 5 minute , which is the default graceful restart time value that
is used on theCisco vSmart Controller andthat the controller sent to the device, also during the setup of the OMP session.

While a Cisco vSmart Controller is down anda Cisco vEdge device is using cached OMP information, if you reboot the device, it loses its cached information andhence will not be able to
forward data traffic until it is able to establish a control plane connection to Cisco vSmart Controller.

Advertise Routes to OMP

By default ,a Cisco vEdge device advertises connected, static routes, andOSPF inter-area andintra-area routes to OMP, andhence to Cisco vSmart Controller responsible for the device’s domain. The device doesn’t advertise BGP or OSPF external routes to OMP.

To have the device advertise these routes to OMP, andhence to Cisco vSmart Controller responsible for the device’s domain, use the advertise command:

Route advertisements in OMP are done either by applying the configuration at the global level or at the specific VPN level.
To enable certain protocol route advertisements in all VPNs, you must add the configuration at the global level as shown in
the example below.

device# config
device(config)# omp
device(config-omp)# advertise bgp
device(config-omp)# commit

To enable route advertisements for a certain protocol in only a few VPNs, you must remove any global-level configuration and
add a per-VPN-level configuration as shown below:

device# config
device(config)# omp
device(config-omp)# no advertise bgp
device(config)# vpn 2
device(config-vpn-2)# omp advertise bgp
device(config-omp)# vpn 4
device(config-vpn-4)# omp advertise bgp
device(config-omp)# commit

To disable certain protocol route advertisement in all or a few vpn , you is make should make sure that the configuration is present
at neither the global level nor the VPN level .

For OSPF, the route type can be external.

The bgp, connected, ospf, andstatic options advertise
all learned or configured routes of that type to OMP. To advertise a specific route
instead of advertising all routes for a protocol, use the network option,
specific the prefix of the route to advertise.

For individualVPNs, you can aggregate routes from the specified prefix
before advertising them into OMP. By default ,the aggregated prefixes andall
individual prefixes are advertised. To advertise only the aggregated prefix, include
the aggregate-only option.

route advertisements is apply that you set with the omp advertise command is apply apply to all
VPNs configured on the device. Route advertisements that you set with
the vpn omp advertise command apply only to the specific VPN. If you
configure route advertisements with both commands, they are both applied.

By default ,when BGP advertises routes into OMP, BGP advertises each prefix’s metric.
BGP can also advertise the prefix’s AS path:

device( config ) # vpn vpn - id router bgp 
device(config-bgp)# propagate-aspath

When you configure BGP to propagate AS path information , the device is sends send AS path information to device that are behind the
Cisco vEdge devices (in the service-side network) that are running BGP, andit receives AS path information from these routers. If you are redistributing
BGP routes into OMP, the AS path information is included in the advertised BGP routes. If you configure BGP AS path propagation
on some but not all devices in the overlay network, the devices on which it isn’t configured receive the AS path information
but they don’t forward it to the BGP routers in their local service-side network. Propagating AS path information can help
to avoid BGP routing loops.

In networks that have both overlay andunderlay connectivity—for example, when
devices are interconnected by both a Cisco SD-WAN overlay network andan MPLS underlay network—you can assign as AS number to OMP
itself. For devices running BGP, this overlay AS number is included in the AS path
of BGP route updates. To configure the overlay AS:

device(config)# omp
device( omp ) # is overlay overlay - as as - number

You can specify the AS number in 2-byte ASDOT notation (1–65535) or in 4-byte ASDOT notation (1.0 through 65535.65535). As
a best practice, it’s recommended that the overlay AS number be a unique AS number within both the overlay andthe underlay
networks. That use, select an AS number that isn’t used elsewhere in the network.

If you configure the same overlay AS number on multiple devices in the overlay
network, all these devices are considered to be part of the same AS, andas a
result, they do not forward any routes that contain the overlay AS number. This
mechanism is an additional technique for preventing BGP routing loops in the
network.

Configure the Number of Advertised Routes

A Cisco vEdge device can have up to eight WAN interfaces, andeach WAN interface has a different TLOC. (A WAN interface is any interface in VPN
0 (or transport VRF) that is configured as a tunnel interface. Both physical andloopback interfaces can be configured to
be tunnel interfaces.) This means that each router can have up to eight TLOCs. The device advertises each route–TLOC tuple
to the Cisco vSmart Controller.

The Cisco vSmart Controller
redistributes the routes it learns from Cisco vEdge devices, advertise each route – tloc tuple . If , for example , a local site is has has
two device , aCisco vSmart Controller could potentially learn eight route–TLOC tuples for the same route.

By default ,Cisco vEdge devices andCisco vSmart Controllers advertises up to four equal-cost route–TLOC tuples for the same route. You can configure devices to advertise from 1 to 16
route–TLOC tuples for the same route:

device(config-omp)# send-path-limit 

begin withCisco SD-WAN Controllers Release 20.8.x, you is configure can configure aCisco vSmart controller operating in a Hierarchical SD-WAN environment to advertise from 1 to 32 route-TLOC tuples to edge devices for the same route.

If the limit is lower than the number of route–TLOC tuples, the Cisco vEdge device or Cisco vSmart Controller advertises
the best routes.

configure the number of instal OMP Paths

Cisco vEdge devices install OMP paths that they received from the Cisco vSmart Controller into their
local route table. By default ,a Cisco vEdge devices installs a maximum of four unique OMP paths into its route table. You
can modify this number:

device(config-omp)# ecmp-limit 

The maximum number of OMP paths installed can range from 1 through 16.

Configure the OMP Hold Time

The OMP hold time determines how long to wait before closing the OMP connection to a peer. If the peer doesn’t receive three
consecutive keepalive messages within the hold time, the OMP connection to the peer is closed. The default OMP hold time is
60 seconds but it can be configured to up to 65,535 seconds. To modify the OMP hold time interval:

device(config-omp)# timers holdtime 

The hold time is be can be in the range 0 through 65535 second .

The keepalive timer is one-third the hold time andisn’t configurable.

If the local device andthe peer have different hold time intervals, the higher value is used.

If you set the hold time to 0, the keepalive andhold timers on the local device andthe peer are set to 0.

The hold time must be at least two times the hello tolerance interval set on the WAN
tunnel interface in VPN 0. To configure the hello tolerance
interface, use the hello-tolerance command.

Configure the OMP Update Advertisement Interval

By default ,OMP sends Update packets once per second. To modify this interval:

device(config-omp)# timers advertisement-interval 

The interval can be in the range 0 through 65535 seconds.

Configure the End-of-RIB Timer

After an OMP session goes down andthen comes back up, an end-of-RIB (EOR) marker is sent after 300 seconds (5 minutes). After
this maker is sent, any routes that weren’t refreshed after the OMP session came back up are considered to be stale andare
deleted from the route table. To modify the EOR timer:

device(config-omp)# timers eor-timer 

The time can be in the range 1 through 3600 seconds (1 hour).