Dynamic Routing
The following two dynamic routing protocols are supported by Citrix SD-WAN:
- Open Shortest Path First (OSPF)
- Border Gateway Protocol (BGP)
Prior to Citrix SD-WAN 11.3.1 release, the dynamic routing capabilities were available only for a single router ID. You can configure a unique router ID either globally for the entire protocol (one for OSPF and BGP) or provide no router ID. If a router ID is not provided, the lowest IP of the Virtual Network Instances (VNIs) participating in dynamic routing is auto-selected as the default router ID.
From Citrix SD-WAN 11.3.1 release onwards, you can not only configure a router ID for the entire protocol but also configure a router ID for each routing domain. With this enhancement, you can enable stable dynamic routing across multiple instances with different router ID’s converging in a stable manner.
If you configure a router ID for a specific routing domain, the specific router ID overrides the protocol level routing domain.
OSPF
OSPF is a routing protocol developed for Internet Protocol (IP) networks by the Interior Gateway Protocol (IGP) group of the Internet Engineering Task Force (IETF). It includes the early version of OSI’s Intermediate System to Intermediate System (IS-IS) routing protocol.
OSPF protocol is open, which means that its specification is in the public domain (RFC 1247). OSPF is based on the Shortest Path First (SPF) algorithm called Dijkstra. It is a link-state routing protocol that calls for sending Link-State Advertisements (LSAs) to all other routers within the same hierarchical area. Information on attached interfaces, metrics used, and other variables are included in OSPF LSAs. OSPF routers accumulate link-state information, which is used by the SPF algorithm to calculate the shortest path to each node.
You can now configure Citrix SD-WAN appliances (Standard and Premium (Enterprise) Editions) to learn routes and advertise routes using OSPF.
Note
Citrix SD-WAN appliances do not participate as Designated Router (DR) and BDR (Backup Designated Router) on each multi-access network since the default DR priority is set to “0.”
Citrix SD-WAN appliance does not support summarization as an Area Border Router (ABR).
Configure OSPF
To configure OSPF:
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In the Configuration Editor, navigate to Connections > Region > Site > OSPF > Basic Settings.
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Click Enable, select, or enter values for the following parameters and click Apply.
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Advertise Citrix SD-WAN Routes: Allow Citrix SD-WAN routes to be advertised via OSPF. You can also specify a tag for OSPF redistribution.
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Advertise BGP Routes: Allow routes learned from BGP peers to be advertised via OSPF. You can also specify a tag for OSPF redistribution.
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Router ID: The unique router identifier, the router is used for OSPF advertisements. If the Router ID is not specified, it is auto-selected as the lowest Virtual IP hosted in the SD-WAN network.
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Export OSPF Route Type: Advertise the Citrix SD-WAN routes to OSPF peers as intra-area routes or external routes.
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Export OSPF Route Weight: When exporting Citrix SD-WAN routes to OSPF, add this weight to each route’s Citrix SD-WAN cost.
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Protocol Preference: If prefixes are learned via multiple routing protocols, the protocol preference value determines routing protocol selection. For more information, see Protocol preference.
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Expand OSPF -> Area, and click Edit.
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Enter an area ID to learn routes from and advertise to.
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If Identity is not checked for a specific Virtual IP Address, the associated Virtual Interface is not available for IP services.
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Choose one of the available Virtual Interfaces from the Name menu. The Virtual Interface determines the Source IP Address.
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Enter the Interface Cost (10 is the default).
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Choose an Authentication Type from the menu.
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If you chose Password or MD5 in step 8, enter the Password associated text field.
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In the Hello Interval field, enter the amount of time to wait between sending Hello protocol packets to directly connected neighbors (10 seconds is the default).
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In the Dead Interval field, enter the interval to wait before marking a router as dead. The default dead interval is 40 seconds.
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Click Apply to save your changes.
Stub area
Stub areas are shielded from external routes and receive information about networks that belong to other areas of the same OSPF domain.
Enable the Stub Area check box.
OSPF redistribution tags
You can use OSPF tags to prevent routing loops during mutual redistributing between OSPF and other protocols. In the OSPF domain, if there are SD-WAN and BGP learned routes to the same subnet, the OSPF loop prevention mechanism identifies it as a loop and ignores the routes. Specifying different tags for SD-WAN and BGP learned routes allows these routes to be installed in the OSPF routing table. You can configure the OSPF redistribution tags for routes learned through SD-WAN and BGP in the OSPF, Basic Settings section.
BGP
BGP is an inter-autonomous system routing protocol. An autonomous network or group of networks is managed under a common administration and with common routing policies. BGP is used to exchange routing information for the Internet and is the protocol used between ISPs. Customer networks deploy Interior gateway protocols such as RIP or OSPF for the exchange of routing information within their networks. Customers connect to ISPs, and ISPs use BGP to exchange customer and ISP routes. When BGP is used between Autonomous Systems (AS), the protocol is called External BGP (EBGP). If a service provider is using BGP to exchange routes within an AS, then the protocol is called Interior BGP (IBGP).
BGP is a robust and scalable routing protocol deployed on the Internet. To achieve scalability, BGP uses many route parameters called attributes to define routing policies and maintain a stable routing environment. BGP neighbors exchange full routing information when the TCP connection between neighbors is first established. When changes to the routing table are detected, the BGP routers send to their neighbors only those routes that have changed. BGP routers do not send periodic routing updates, and advertise only the optimal path to a destination network. You can configure Citrix SD-WAN appliances to learn routes and advertise routes using BGP.
Configure BGP
To configure BGP:
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In the Configuration Editor, navigate to Connections > Region > Site > BGP > Basic Settings.
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Click Enable, select, or enter values for the following parameters and click Apply.
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Advertise Citrix SD-WAN Routes: Allow Citrix SD-WAN routes to be advertised via BGP.
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Advertise OSPF Routes: Allow routes learned from OSPF peers to be advertised via BGP.
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Router ID: The unique router identifier, the router is used for OSPF advertisements. If the Router ID is not specified, it is auto-selected as the lowest Virtual IP hosted in the SD-WAN network.
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Local Autonomous System: The local autonomous system number from which the routes are learned and advertised to. The autonomous system number must match with one on the neighboring routers.
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Protocol Preference: If prefixes are learned via multiple routing protocols, the protocol preference value determines routing protocol selection. For more information, see Protocol preference.
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Expand Basic Settings > Neighbors and click the Add (+) icon.
For Sites with multiple Routing Domains choose a routing domain. Routing Domain determines which Virtual Interfaces are available.
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Choose a Virtual Interface from the menu. The Virtual Interface determines the Source IP Address.
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Enter the IP Address of the IBGP Neighbor router in the Neighbor IP field, and Local Autonomous System number in the Neighbor AS field.
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In the Hold Time (s) field, enter the Hold Time, in seconds, to wait before declaring a neighbor down (the default is 180).
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In the Local Preference (s) field, enter the Local Preference value, in seconds, which is used for selection from multiple BGP routes (the default is 100).
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Click the IGP Metric check box to enable the comparison of internal distances to calculate the best route.
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Click the Multi-hop check box to enable multiple hops for the route.
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In the Password field, enter a password for MD5 authentication of BGP sessions (authentication is not required).
Note
Configuring Route Reflectors and Confederations for iBGP is not supported in SD-WAN network.
Exterior BGP (eBGP)
Citrix SD-WAN appliances connect to a switch on the LAN side and a Router on the WAN side. As SD-WAN technology starts becoming more integral to Enterprise network deployments, SD-WAN appliances replace the Routers. SD-WAN implements eBGP dynamic routing protocol to function as a dedicated routing device.
SD-WAN appliance establishes a neighborship with peer routers using eBGP towards WAN side and is able to learn, advertise routes from and to peers. You can select importing and exporting eBGP learned routes on peer devices. Also, SD-WAN static, virtual path learned routes can be configured to advertise to eBGP peers.
For more information, see the following use cases:
- SD-WAN site Communicating with non-SD-WAN site over eBGP
- Communication Between SD-WAN sites Using Virtual Path and eBGP
- Implementing OSPF in one-arm topology
- OSPF Type5 to Type1 deployment in MPLS Network
- SD-WAN and non-SD-WAN (third-party) appliance OSPF deployment
- Implementing OSPF using SD-WAN network with high-availability setup
AS path length
BGP protocol uses the AS path length attribute to determine the best route. The AS path length indicates the number of autonomous systems traversed in a route. Citrix SD-WAN uses the BGP AS path length attribute to filter and import routes.
Non-SD-WAN appliances can choose to route traffic to Primary DC or Secondary DC SD-WAN appliances by importing routes based on their AS path length. You can also dynamically steer traffic from a router to Secondary DC by simply increasing the AS path length of the Primary DC appliance on the router, making it unpreferable. Eliminating the need to change the route cost and perform a configuration update.
To configure AS path length in import filters, select BGP as the protocol, select a predicate, and enter the AS path length. For more information, see Route Filtering
Monitor route statistics
Navigate to Monitor > Statistics. Select Routes from the Show drop-down menu.
All functions for applicable Routes are supported in Citrix SD-WAN network regardless of whether a Route is Dynamic or Static.
