Changing Route Preferences to Migrate to Another IGP
Problem
You are migrating the IGP on your network from OSPF to IS-IS and you want to do this in a controlled manner.
Solution
After configuring both OSPF and IS-IS on the routers you are migrating, change the route preference on the OSPF routes to be higher than the IS-IS preference:
[edit protocols ospf] aviva@Router3# set preference 175
Discussion
While you can change the preference values for all dynamic routing protocols and user-configured routes using the set preference and set external-preference commands when configuring the protocols, it is generally not a good idea. The changes you make affect only the router you are configuring, and the local router will end up with a different idea of relative route preferences than the other routers on the network. Also, changing route preferences could affect which routes become active, which, in turn, would affect which routes are used to forward traffic.
However, one situation where you might want to change route preferences is when migrating IGPs. In this recipe, we are migrating from using OSPF as the IGP to using IS-IS. A preference of 175 for OSPF is greater than that of any IS-IS routes. From Table 8-2, you see that IS-IS internal routes have a preference of either 15 (for Level 1) or 18 (for Level 2), and external routes have a preference of 160 (for Level 1) or 165 (for Level 2).
The command shown in this recipe is actually the last step in an OSPF-to-IS-IS migration strategy. The first step is to configure IS-IS on the same interfaces that are running OSPF (see Recipe 11.1), then verify that IS-IS adjacencies are established on the same interfaces that have OSPF adjacencies:
aviva@Router3> show isis adjacency Interface System L State Hold (secs) SNPA so-0/2/0.0 R1 2 Up 20 so-0/2/1.0 R2 2 Up 21 so-0/2/2.0 R4 2 Up 19 so-0/2/3.0 R10 2 Up 19 aviva@Router3> show ospf neighbor Address Interface State ID Pri Dead 10.1.2.1 so-0/2/0.0 Full 10.10.255.1 128 36 10.1.6.1 so-0/2/1.0 Full 10.10.255.2 128 38 10.1.7.2 so-0/2/2.0 Full 10.10.255.4 128 34 10.1.8.2 so-0/2/3.0 Full 10.10.255.10 128 38
You then need to ensure that IS-IS calculates the same paths as OSPF. The default IS-IS metrics must be changed so that they give the same relative cost to each path as does OSPF. You can do this by manually assigning appropriate interface metrics or by configuring a reference bandwidth. (See Recipe 11.10 for IS-IS and Recipe 12.11 for OSPF.)
Unlike OSPF, for which the JUNOS software has an automatic costing algorithm based on interface bandwidth, for IS-IS JUNOS software assigns a default metric of 10 to all IS-IS interfaces. If this default is left unchanged, the shortest paths calculated by IS-IS are essentially shortest-hop paths.
With IS-IS enabled and metrics configured correctly, the routing table should have the same number of IS-IS entries as OSPF entries for each destination, and they should point to the same outgoing next hops. That is, if there is one OSPF route to a prefix, there should be one IS-IS route to the same prefix and with the same outgoing interface. If there are two OSPF routes to a prefix, there should be two IS-IS routes, and so on.
aviva@Router3> show route inet.0: 28 destinations, 48 routes (28 active, 0 holddown, 0 hidden) Restart Complete + = Active Route, - = Last Active, * = Both 10.1.1.0/24 *[OSPF/10] 00:16:20, metric 65 via so-0/2/0.0 > via so-0/2/1.0 [IS-IS/18] 00:16:08, metric 126 to 10.1.2.1 via so-0/2/0.0 > to 10.1.6.1 via so-0/2/1.0 10.1.3.0/24 *[OSPF/10] 00:16:20, metric 65 via so-0/2/0.0 > via so-0/2/2.0 [IS-IS/18] 00:16:08, metric 126 > to 10.1.2.1 via so-0/2/0.0 to 10.1.7.2 via so-0/2/2.0 …
The output shows that for each destination prefix, OSPF and IS-IS have the same number of routes and the same outgoing interfaces. The preferred route for each prefix (marked with an *) is the OSPF route. If there are equal-cost paths, the next hop chosen by OSPF (>) is not always the same as that chosen by IS-IS. This will not cause routing problems as long as the equal-cost paths are consistent between the protocols.
At this point, you change the route preference using the set protocols ospf preference command shown in this recipe. Here, you increase the OSPF preference to a value higher than any of the IS-IS preferences because OSPF is the protocol that you are migrating away from. You could instead change the IS-IS route preference so that its routes are more preferred than OSPF. However, leaving the IS-IS preference at its default value simplifies any future addition of routers to the network. Another alternative at this point would be to delete OSPF from the configuration altogether. However, you should leave it in for a short period of time to test the migration. If there are any problems and you need to back out of the migration, all you need to do is return to the default OSPF preference value:
[edit protocols ospf] aviva@Router3# delete preference aviva@Router3# commit
To verify the preference change, look at the routing table to check that IS-IS is the preferred protocol for all the routes:
aviva@Router3> show route inet.0: 28 destinations, 48 routes (28 active, 0 holddown, 0 hidden) Restart Complete + = Active Route, - = Last Active, * = Both 10.1.1.0/24 *[IS-IS/18] 00:32:24, metric 126 to 10.1.2.1 via so-0/2/0.0 > to 10.1.6.1 via so-0/2/1.0 [OSPF/175] 00:01:48, metric 65 via so-0/2/0.0 > via so-0/2/1.0 10.1.3.0/24 *[IS-IS/18] 00:32:24, metric 126 > to 10.1.2.1 via so-0/2/0.0 to 10.1.7.2 via so-0/2/2.0 [OSPF/175] 00:01:48, metric 65 > via so-0/2/0.0 via so-0/2/2.0
When you are sure that IS-IS is working properly, remove the OSPF configuration from the router:
[edit protocols] aviva@Router3# delete ospf aviva@Router3# commit
See Also
Recipes 11.1, 11.10, 12.1, and 12.11
Router Configuration and File Management
- Introduction
- Configuring the Router for the First Time
- Configuring the Router from the CLI
- Getting Exclusive Access to Configure the Router
- Displaying the Commands to Recreate a Configuration
- Including Comments in the Configuration
- Checking the Syntax of the Configuration
- Activating the Router Configuration
- Debugging a Failed Commit
- Exiting Configuration Mode
- Keeping a Record of Configuration Changes
- Determining What Changes You Have Made to the Configuration
- Configuring the Router by Copying a File from a Server
- Configuring the Router by Copying Text from a Terminal Window
- Backing Up the Routers Configuration
- Scheduling the Activation of a Configuration
- Provisionally Activating a Configuration
- Loading a Previous Router Configuration
- Creating an Emergency Rescue Configuration
- Backing Up Filesystems on M-Series and T-Series Routers
- Backing Up Filesystems on J-Series Routers
- Restoring a Backed-Up Filesystem
- Installing a Different Software Release on M-Series and T-Series Routers
- Installing a Different Software Release on J-Series Routers
- Creating an Emergency Boot Disk
- Gathering Software Version Information
- Gathering Hardware Inventory Information
- Finding Out How Long the Router Has Been Up
- Gathering Information Before Contacting Support
- Managing Routers with Similar Configurations
- Managing Redundant Routing Engines
- Using the Second Routing Engine to Upgrade to a New Software Version
Basic Router Security and Access Control
- Basic Router Security and Access Control
- Introduction
- Allowing Access to the Router
- Controlling Root Authentication
- Logging In to the Routers Console
- Setting the Login Authentication Methods
- Setting Up Login Accounts on the Router
- Changing the Format of Plain-Text Passwords
- Changing the Plain-Text Password Encryption Method
- Creating a Login Account for Remote Authentication
- Creating a Group Login Account
- Customizing Account Privileges
- Creating a Privilege Class that Hides Encrypted Passwords
- Setting Up RADIUS User Authentication
- Setting Up TACACS+ User Authentication
- Restricting Inbound SSH and Telnet Access
- Setting the Source Address for Telnet Connections
- Creating a Login Banner
- Finding Out Who Is Logged In to the Router
- Logging Out of the Router
- Forcibly Logging a User Out
IPSec
- IPSec
- Introduction
- Configuring IPSec
- Configuring IPSec Dynamic SAs
- Creating IPSec Dynamic SAs on J-Series Routers or Routers with AS PICs
- Using Digital Certificates to Create Dynamic IPSec SAs
SNMP
- SNMP
- Introduction
- Configuring SNMP
- Setting Router Information for the MIB-II System Group
- Setting Up SNMP Traps
- Controlling SNMP Access to the Router
- Using a Firewall Filter to Protect SNMP Access
- Controlling Access to Router MIBs
- Extracting Software Inventory Information with SNMP
- Extracting Hardware Inventory Information with SNMP
- Collecting Router Operational Information with SNMP
- Logging SNMP Access to the Router
- Logging Enterprise-Specific Traps
- Using RMON Traps to Monitor the Routers Temperature
- Configuring SNMPv3
- Tracking Router Configuration Changes
- Setting Up SNMPv3 Traps
Logging
- Logging
- Introduction
- Turning On Logging
- Limiting the Messages Collected
- Including the Facility and Severity in Messages
- Changing the Size of a Logging File
- Clearing the Routers Logfiles
- Sending Log Messages to Your Screen
- Sending Logging Messages to a Log Server
- Saving Logging Messages to the Other Routing Engine
- Turning Off Logging
- Turning On Basic Tracing
- Monitoring Interface Traffic
NTP
- NTP
- Introduction
- Setting the Date and Time on the Router Manually
- Setting the Time Zone
- Synchronizing Time When the Router Boots
- Synchronizing Time Periodically
- Authenticating NTP
- Checking NTP Status
Router Interfaces
- Router Interfaces
- Introduction
- Viewing Interface Status
- Viewing Traffic Statistics on an Interface
- Setting an IP Address for the Router
- Setting the Routers Source Address
- Configuring an IPv4 Address on an Interface
- Configuring an IPv6 Address on an Interface
- Configuring an ISO Address on an Interface
- Creating an MPLS Protocol Family on a Logical Interface
- Configuring an Interface Description
- Choosing Primary and Preferred Interface Addresses
- Using the Management Interface
- Finding Out What IP Addresses Are Used on the Router
- Configuring Ethernet Interfaces
- Using VRRP on Ethernet Interfaces
- Connecting to an Ethernet Switch
- Configuring T1 Interfaces
- Performing a Loopback Test on a T1 Interface
- Setting Up a BERT Test on a T1 Interface
- Configuring Frame Relay on a T1 Interface
- Configuring a SONET Interface
- Using APS to Protect Against SONET Circuit Failures
- Configuring an ATM Interface
- Dealing with Nonconfigurable Interfaces
- Configuring Interfaces Before the PICs Are Installed
IP Routing
- IP Routing
- Introduction
- Viewing the Routes in the Routing Table
- Viewing Routes to a Particular Prefix
- Viewing Routes Learned from a Specific Protocol
- Displaying the Routes in the Forwarding Table
- Creating Static Routes
- Blackholing Routes
- Filtering Traffic Using Unicast Reverse-Path Forwarding
- Aggregating Routes
- Load-Balancing Traffic Flows
- Adding Martian Addresses
- Changing Route Preferences to Migrate to Another IGP
- Configuring Routing Protocols to Restart Without Losing Adjacencies
Routing Policy and Firewall Filters
- Routing Policy and Firewall Filters
- Introduction
- Creating a Simple Routing Policy
- Changing a Routes Routing Information
- Filtering Routes by IP Address
- Filtering Long Prefixes
- Filtering Unallocated Prefix Blocks
- Creating a Chain of Routing Policies
- Making Sure a Routing Policy Is Functioning Properly
- Creating a Simple Firewall Filter that Matches Packet Contents
- Creating a Firewall Filter that Negates a Match
- Reordering Firewall Terms
- Filtering Traffic Transiting the Router
- Using a Firewall Filter to Count Traffic on an Interface
- Logging the Traffic on an Interface
- Limiting Traffic on an Interface
- Protecting the Local Routing Engine
- Rate-Limiting Traffic Flow to the Routing Engine
- Using Counters to Determine Whether a Router Is Under Attack
RIP
- RIP
- Introduction
- Configuring RIP
- Having RIP Advertise Its Routes
- Configuring RIP for IPv6
- Enabling RIP Authentication
- Routing RIP Traffic over Faster Interfaces
- Sending Version 1 Update Messages
- Tracing RIP Protocol Traffic
IS-IS
- IS-IS
- Introduction
- Configuring IS-IS
- Viewing the IS-IS Link-State Database
- Viewing Routes Learned by IS-IS
- Configuring IS-IS for IPv6
- Configuring a Level 1Only Router
- Controlling DIS Election
- Enabling IS-IS Authentication
- Redistributing Static Routes into IS-IS
- Leaking IS-IS Level 2 Routes into Level 1
- Adjusting IS-IS Link Costs
- Improving IS-IS Convergence Times
- Moving IS-IS Traffic off a Router
- Disabling IS-IS on an Interface
- Tracing IS-IS Protocol Traffic
OSPF
- Introduction
- Configuring OSPF
- Viewing Routes Learned by OSPF
- Viewing the OSPF Link-State Database
- Configuring OSPF for IPv6
- Configuring a Multiarea OSPF Network
- Setting Up Stub Areas
- Creating a Not-So-Stubby Area
- Summarizing Routes in OSPF
- Enabling OSPF Authentication
- Redistributing Static Routes into OSPF
- Adjusting OSPF Link Costs
- Improving OSPF Convergence Times
- Moving OSPF Traffic off a Router
- Disabling OSPF on an Interface
- Tracing OSPF Protocol Traffic
BGP
- Introduction
- Configuring a BGP Session Between Routers in Two ASs
- Configuring BGP on Routers Within an AS
- Diagnosing TCP Session Problems
- Adjusting the Next-Hop Attribute
- Adjusting Local Preference Values
- Removing Private AS Numbers from the AS Path
- Prepending AS Numbers to the AS Path
- Filtering BGP Routes Based on AS Paths
- Restricting the Number of Routes Advertised to a BGP Peer
- Authenticating BGP Peers
- Setting Up Route Reflectors
- Mitigating Route Instabilities with Route Flap Damping
- Adding a BGP Community to Routes
- Load-Balancing BGP Traffic
- Tracing BGP Protocol Traffic
MPLS
- Introduction
- Configuring LSPs Using LDP as the Signaling Protocol
- Viewing Information and LDP-Signaled LSPs in the Routing Tables
- Verifying that an LDP-Signaled LSP Is Carrying Traffic
- Enabling LDP Authentication
- Tracing LDP Operations
- Setting Up RSVP-Signaled LSPs
- Viewing Information About RSVP-Signaled LSPs in the Routing Tables
- Verifying Packet Labels
- Verifying that the RSVP-Signaled LSP Is Carrying Traffic
- Configuring RSVP Authentication
- Protecting an LSPs Path
- Using Fast Reroute to Reduce Packet Loss Following a Link Failure
- Automatically Allocating Bandwidth
- Prioritizing LSPs
- Allowing IGP Traffic to Use an LSP
- Installing LSPs into the Unicast Routing Table
- Tracing RSVP Operations
VPNs
- Introduction
- Setting Up a Simple Layer 3 VPN
- Viewing the VPN Routing Tables
- Adding a VPN for a Second Customer
IP Multicast
- Introduction
- Configuring PIM-SM
- Manually Establishing a PIM-SM RP
- Using Auto-RP to Dynamically Map RPs
- Setting Up a PIM-SM Bootstrap Router
- Filtering PIM-SM Bootstrap Messages
- Configuring Multiple RPs in a PIM-SM Domain with Anycast RP
- Configuring Multiple RPs in a PIM-SM Domain Anycast PIM
- Limiting the Group Ranges an RP Services
- Viewing Multicast Routes
- Checking the Groups for Which a PIM-SM Router Maintains Join State
- Manually Configuring IGMP
- Using SSM
- Connecting PIM-SM Domains Using MSDP and MBGP
- Configuring PIM-DM
- Tracing PIM Packets
EAN: 2147483647
Pages: 290
- An Emerging Strategy for E-Business IT Governance
- Assessing Business-IT Alignment Maturity
- Linking the IT Balanced Scorecard to the Business Objectives at a Major Canadian Financial Group
- Measuring and Managing E-Business Initiatives Through the Balanced Scorecard
- Technical Issues Related to IT Governance Tactics: Product Metrics, Measurements and Process Control
