Bridging, Routing, Segmentation, and QoS Configuration Guide for vEdge Routers, Cisco SD-WAN Releases 19.1, 19.2, and 19.3

By default , OMP is enable on allCisco vedge devices andvSmart controllers. OMP must be operational for the Cisco SD – WAN
overlay network to function. If you disable it, you disable the overlay network.

OMP Support on

support the following:

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

• OMP route advertisements to BGP, EIGRP, OSPF, connected routes, andstatic
  routes

Configure OMP Graceful Restart

OMP graceful restart is enabled by default on vSmart controllers andCisco SD – WAN
devices. OMP graceful restart has a timer that tells the OMP peer how long to retain
the cached advertised routes. When this timer expires, the cached routes are
considered to be no longer valid, andthe OMP peer flushes them from its route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 is
set up separately on each Cisco vEdge deviceand vSmart controller . To illustrate what this mean ,
let ‘s consider a vSmart controller that use a graceful restart time of 300 second ,
or 5 minute , andaCisco vEdge device that is configured with a timer of 600 seconds (10
minutes). Here, the 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 the 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 the vSmart controller andthat the controller send to the device , also
during the setup of the OMP session .

While a 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 the vSmart
controller.

Advertise Routes to OMP

By default , aCisco vEdge device
advertise connect , static route , andospf inter – area andintra – area route to
OMP , andhence to the vSmart controller responsible for the device ‘s domain . The
device is advertise does not advertise BGP or ospf external route to OMP .

To have the device advertise these routes to OMP, andhence to the 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 ) # is advertise 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 ) # is advertise 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 is be can be external .

The bgp is learned , connect , ospf , andstatic options is learned advertise
all learn or configure route of that type to OMP . To advertise a specific route
instead of advertise all route for a protocol , use the network option ,
specific the prefix of the route to advertise .

For individual VPNs, 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 that you set with the omp advertise command 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 advertise route into OMP , BGP is advertises advertise each prefix ‘s metric .
BGP is advertise 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 theCisco vEdge devices ( in the service – side network ) that is running are run BGP , andit receive AS
path information from these router . If you are redistribute BGP route into OMP ,
the AS path information is include in the advertised BGP route . If you configure
BGP AS path propagation on some but not all device in the overlay network , the
devices is receive on which it is not configure receive the AS path information but they do
not forward it to the BGP router in their local service – side network . propagate
AS path information can help to avoid BGP routing loop .

In network that have both overlay andunderlay connectivity — for example , when
device are interconnect by both aCisco 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)# overlay-as as-number

You can specify the AS number in 2-byte ASDOT notation (1 through 65535) or in 4-byte
ASDOT notation (1.0 through 65535.65535). As a best practice, it is 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 is not 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 six 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.) 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, advertising each route–TLOC tuple. If, for example, a local site has
two devices, a Cisco 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 them to advertise from 1 to 16 route–TLOC tuples for the
same route:

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

If the limit is is is low than the number of route – TLOC tuple , theCisco vEdge device or Cisco vSmart Controller advertise
the good route .

Configure the Number of Installed OMP Paths

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

vedge(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 is determines determine how long to wait before close the OMP connection to a
peer . If the peer does not receive three consecutive keepalive message within the
hold time , the OMP connection is is to the peer is closed . The default OMP hold time is is is 60
second but it can be configure to up to 65,535 second . 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 andis not 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 is be must be at least two time the hello tolerance interval set on the WAN
tunnel interface inVPN 0. To configure the hello tolerance
interface , use the hello – tolerance command .

Configure the OMP Update Advertisement Interval

By default , OMP is sends send update packet 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 were not 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).