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1NANAOG24 © 2001, Cisco Systems, Inc. All rights reserved.© 2001, Cisco Systems, Inc. All rights reserved.© 2002, Cisco Systems, Inc. All rights reserved.
IS-IS Deployment, Design Guidelines and New Features
Shankar [email protected]
Internet Engineering Support
222NANOG24 © 2002, Cisco Systems, Inc. All rights reserved.
Agenda
• Scope of the Presentation
• Deployment ScenariosL1-Only
L2-Only
L1 & L2 With Route Leaking
• Design Considerations Set Over Load Bit
LSP Flooding
SPF PRC LSP Generation and MORE
• New FeaturesRoute Leaking
Route Tags
Extensions to MPLS-TE and MORE
333NANOG24 © 2002, Cisco Systems, Inc. All rights reserved.
Scope of the Presentation
• Cover the Deployment Scenarios adopted by the ISPs in deploying IS-IS.
• Talk about the Design Guidelines which applies to the different deployment scenarios .
• Also cover the recent new enhancements to the IS-IS Protocol.
444NANOG24 © 2002, Cisco Systems, Inc. All rights reserved.
Why IS-IS ?
• Embraced by the large tier1 ISPs.
• Proven to be a very stable and scalable, with very fast convergence.
• Encodes the packet(s) in TLV format.
• Flexible protocol in terms of tuning and easily extensible to new features (MPLS-TE etc).
• It runs directly over Layer 2. (next to IP).
5NANAOG24 © 2001, Cisco Systems, Inc. All rights reserved.© 2001, Cisco Systems, Inc. All rights reserved.© 2002, Cisco Systems, Inc. All rights reserved.
Deployment Scenarios
666NANOG24 © 2002, Cisco Systems, Inc. All rights reserved.
L1-Only POPs
POP 1L1-Only
POP 3L1-Only
COREL1-Only
POP 4L1-Only
POP 2L1-Only
777NANOG24 © 2002, Cisco Systems, Inc. All rights reserved.
L1-Only POPs (Cont.)
• IS-IS is a newer protocol at that time at least operationally with the ISPs
• In this design—all the routers will be running in one area and are all doing L1-only routing
• This design is flat with a single L1-only database running on all the routers
• If you have a change in the topology, the SPF computation will be done in all the routers as they are in the L1-only sub-domain
888NANOG24 © 2002, Cisco Systems, Inc. All rights reserved.
L1-Only POPs (Cont.)
• Also the Tier 1 ISPs picked up L1-only to avoid sub-optimal routing problems [before Route-Leaking]
• The other factor is when the router runs as L1L2—then the router(s) will have 2 instances of SPFs
• Since most of the routers were AGS+/7XXX at that time, the ISPs had chosen L1-only single-area IS-IS with in their network
999NANOG24 © 2002, Cisco Systems, Inc. All rights reserved.
L2-Only POPs (all in the same area)
POP 1Area 49.0001
POP 3Area 49.0001
POP 2Area 49.0001
COREL2-Only
POP 4Area 49.0001
101010NANOG24 © 2002, Cisco Systems, Inc. All rights reserved.
L2-Only POPs (Each POP in a different area)
POP 1Area 49.0001
POP 3Area 49.0003
POP 2Area 49.0002
CORE
L2-ONLY
POP 4Area 49.0004
111111NANOG24 © 2002, Cisco Systems, Inc. All rights reserved.
L2-Only POPs (Cont.)
• Most of the Tier 1 ISPs are running Level 2-only on all the routers [mid 90’s to late 90’s]
• The rough approximation of routers L2-only are about 800–1000
• The SPF-computation may take up to ~150 msecs. [ for +/- 1200 routers ]
• Most of the uplinks into the core are OC-12 to OC-192 POS links
• As the network grows, easy to bring the L1-only POPs for easy migration.
• All the routers in L2 will share all the LSPs
121212NANOG24 © 2002, Cisco Systems, Inc. All rights reserved.
L2-Only POPs (Cont.)
• A typical optimized IS-IS configuration that a tier1 ISP uses:
set-overload-bit [on-startup [<timeout> | wait-for-bgp] ] max-lsp-lifetime 65535 isp-refresh-interval 65000 spf-interval 10 prc-interval metric-style wide [no] hello-padding [either turned globally or
per-interface basis]
log-adjacency-changes ignore-lsp-errors
131313NANOG24 © 2002, Cisco Systems, Inc. All rights reserved.
L1 in the POP and L2 in the Core
POP 1L1-Only
Area 49.0001
POP 3L1-Only
Area 49.0003
POP 2L1-Only
Area 49.0002
COREL2-Only
Area 49.0005
POP 4L1-Only
Area 49.0004
L1L2L1L2
L1L2L1L2
L1L2L1L2
L1L2L1L2
L1L2L1L2
L1L2L1L2L1L2L1L2
L1L2L1L2
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L1 in the POP and L2 in the Core (Cont.)
• Within a given local pop—all the routers will be in a separate area
• The L1L2 routers at the edge of the POPs will be running
L1-adj going into the POP
L2-adj into the core with the rest of the L1L2 routers
• The SPF computations will be limited to the respective L1 and L2 Areas only.
• All the L1-routers in a given pop will receive the ATT bit set by the L1L2 router at the edge of this pop
• This may cause the sub-optimal routing in reaching out the prefixes outside the POP by the local routers.
151515NANOG24 © 2002, Cisco Systems, Inc. All rights reserved.
L1 in the POP and L2 in the Core (Cont.)
• It is recommended to configure the L1L2 routers at the edge of the pop with route-leaking capabilities
• This way, we leak the longer prefixes of the remote pop into the local pop
• Hence the L1 routers will be able to take the right exit router based on the metric of the leaked IP-prefix
• Whenever you configure for route-leaking—make sure you configure the routers with metric-style wide
Route-Leaking
16NANAOG24 © 2001, Cisco Systems, Inc. All rights reserved.© 2001, Cisco Systems, Inc. All rights reserved.© 2002, Cisco Systems, Inc. All rights reserved.
Design Considerations
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Set Over Load Bit
• 10589 defines for each LSP a special bit called the LSPDB Over Load Bit
• While having problems, a router could set the OL bit, and other routers would route around it
• Connected IP prefixes still reachable
This may change in the future
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Set Over Load Bit
When R1 computes SPT, it will find That R5 LSP has Overload-bit-set.Therefore R5 cannot be used as Transit node and shortest path to R4 is: R1->R2->R3->R4
• Why/When use Overload-Bit ? When the router is not ready to forward traffic for ALL destinations
Typically when IS-IS is up but BGP (or even MPLS) not up yet.
When the router has other functions (Network Management)
Rtr-1Rtr-2
Rtr-3
Rtr-4
Rtr-5
191919NANOG24 © 2002, Cisco Systems, Inc. All rights reserved.
Set Over Load Bit (Cont.)
• Feature to assist routers in completing their BGP tables after boot-up
• BGP may not have had time to fully converge before receiving traffic
• Therefore router may drop traffic for destinations not learnt yet via BGP
• Better stabilization if router could build its BGP table before fully participating in packet forwarding
202020NANOG24 © 2002, Cisco Systems, Inc. All rights reserved.
Set Over Load Bit (Cont.)
router isis
set-overload-bit
set-overload-bit on-startup <sec>
set-overload-bit on-startup wait-for-bgp
router bgp 100
bgp update-delay <sec>
212121NANOG24 © 2002, Cisco Systems, Inc. All rights reserved.
Set Over Load Bit (Cont.)
• Enhanced configuration:router isis
set-overload-bit [on-startup[<timeout>|wait-for-bgp]]
• New keyword “wait-for-bgp”
• When BGP doesn’t inform IS-IS it is ready and “wait-for-bgp” is configured, the over load bit will be cleared after 10 minutes.
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LSP Flooding
• ISO 10589 states LSP flooding on a LAN should be limited to 30 LSP’s per second
• IOS throttles over both LAN and point-to-point interfaces
• Default time between consecutive LSP’s is a minimum of 33 milliseconds
• On slow speed links, 30 LSP’s per second may be too much
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LSP Flooding (Cont.)
• Time between flooding consecutive LSP’s is configurable:
Rtr-A(config)#int serial0 Rtr-A(config-if)#isis lsp-interval?
<1-4294967295> LSP transmission interval (milliseconds)
• IS-IS will now send LSP’s only up to 50% of the configured bandwidth
• Therefore, advisable to configure the bandwidth parameter on links below T1
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LSP Flooding (Cont.)
• Several interface configuration commands
isis lsp-interval 33 delay between LSP transmission interval (flooding)
(msecs)
isis retransmit-interval 5 delay between retransmissions of the same LSP
(seconds)
isis retransmit-throttle-interval 100 delay between retransmitted LSPs (msecs)
isis mesh-group blocked block LSP flooding on this interface
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LSP Flooding (Cont.)
• LAN flooding usually doesn’t encounter any problem
• No retransmission over LANs
• No ACKs on LANs; DIS only sends periodic CSNPs
• Reduce CSNP timer for faster convergence over a LAN
int ethernet 1/0
isis csnp-interval <0-65535>
262626NANOG24 © 2002, Cisco Systems, Inc. All rights reserved.
LSP Generation: What triggers a new LSP
• When something changes …
adjacency came up or went down
interface up/down (connected IP prefix !)
redistributed IP routes change
inter-area IP routes change
an interface is assigned a new metric
most other configuration changes
periodic refresh
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LSP Generation: New LSP
• Create new LSP, install in your own LSPDB and mark it for flooding
• Send the new LSP to all neighbors
• Neighbors flood the LSP further.
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LSP Generation
• LSP generation (lsp-gen-interval)Control the “frequency” of LSP generation
Prevent from flapping links causing a lot of LSPs to be flooded throughout the network
• IS-IS throttles it main events SPF/PRC computation, LSP generation
• Throttling slows down convergence
• Not throttling can cause melt-downs
• Find a compromise…
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Exponential Backoff:Enhancements to SPF Algorithms
SPFSPF
Incremental-IntervalIncremental-Interval
Initial-WaitInitial-Wait
5.5 Sec5.5 Sec
5.5 Sec5.5 Sec
Maximum-IntervalMaximum-Interval 10 Sec10 Sec
PRCPRC
5 Sec5 Sec
2 Sec2 Sec
5 Sec5 Sec
LSPGeneration
LSPGeneration
5 Sec5 Sec
50 msec50 msec
5 Sec5 Sec
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Exponential Backoff:spf-interval
• Extended syntax
spf-interval <a> [<b> <c>]
<a> seconds between consecutive SPF runs(seconds)
<b> initial wait before the first SPF (msecs)
<c> minimum wait between first and second SPF (msecs)
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Exponential Backoff:spf-interval Example
spf-interval 10 100 1000 (a) (b) (c)
On original trigger a delay of 100 ms is incurred prior
to running SPF.
If a 2nd SPF is required, a delay of at least
1000msecs must expire.
The 3rd SPF can only be run after another 2s, then
4s, then 8s, then 10 sec, 10 sec
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Exponential Backoff:spf-interval Example
• When the network calms down, and there were no triggers for 2 times the minimum interval (20sec in this example), go back to fast behavior (100 ms initial wait)
333333NANOG24 © 2002, Cisco Systems, Inc. All rights reserved.
Exponential Backoff:prc-interval and lsp-gen-interval
• Same Syntax for
prc-interval
lsp-gen-interval
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Hello Padding
• IS-IS by default pads the Hellos to the fullest MTU size to detect the MTU mismatches.
• This results in: Inefficient use of bandwidth
May use significant number of buffers
Processing overhead when using Authentication
353535NANOG24 © 2002, Cisco Systems, Inc. All rights reserved.
Hello Padding
• You can turn on/off the Hello-Padding either per interface level or via globally
• The router isis CLI:
[no] hello padding [multi-point|point-to-point]
• The Interface CLI:
[no] isis hello padding
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TimerTimer Default ValueDefault Value Cisco IOS CommandCisco IOS Command
MaxageMaxage
LSP Refresh IntervalLSP Refresh Interval
LSP Transmission IntervalLSP Transmission Interval
LSP Retransmit IntervalLSP Retransmit Interval
CSNP IntervalCSNP Interval
1200s1200s
900s900s
33ms33ms
5s5s
10s10s
isis max-lsp-Intervalisis max-lsp-Interval
isis refresh-intervalisis refresh-interval
isis lsp-intervalisis lsp-interval
isis retransmit-intervalisis retransmit-interval
isis csnp-intervalisis csnp-interval
Database Timers
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Database Timers (Cont.)
• Note: On high lifetime values
The high lifetime values need to be used carefully
even though they provide robustness in the network.
Using high lifetimes may result in keeping obsolete
information in LSPDB for more time than needed.
Having such useless LSPs in database is harmless
anyway but should be aware of the above drawback.
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Non-Advertisement of Parallel Adjacencies in the LSP
• When building an IS-IS LSP all adjacencies are inserted from the DB
• Parallel adjacencies may therefore be included and advertised in the LSP
• Not necessary—only need to advertise parallel pt2pt adjacencies once
• Only use best connection between two routers for SPF (unequal path metrics)
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Non-Advertisement of Parallel Adjacencies in the LSP (Cont.)
• Number of advantages for not advertising parallel adjacencies
LSP’s will be smaller and use less bandwidth when flooded
LSP’s have lower chances of being fragmented
SPF calculations will be more efficient
Flapping of one of a set of parallel links will be invisible to the rest of the network
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Non-Advertisement of Parallel Adjacencies in the LSP (Cont.)
5
3
32
LSP AIS: 5 BIS: 3 BIS: 3 CIS: 5 D
LSP BIS: 5 AIS: 3 AIS: 6 CIS: 2 D
Only the best Parallel Adjacency is reported
Rtr-BRtr-A
Rtr-C Rtr-D
41NANAOG24 © 2001, Cisco Systems, Inc. All rights reserved.© 2001, Cisco Systems, Inc. All rights reserved.© 2002, Cisco Systems, Inc. All rights reserved.
New Features
424242NANOG24 © 2002, Cisco Systems, Inc. All rights reserved.
Dynamic Host Name
• All ISPs configure STATIC mappings of system-IDs
• This process has dis-adv of maintaining huge (identical) databases on all the routers
• Adding a router to the network, means updating this static mappings on all the routers
• Human mistake(s)
Router-A(config)# clns host <name> <nsap>
434343NANOG24 © 2002, Cisco Systems, Inc. All rights reserved.
Dynamic Host Name (Cont.)
• A New TLV 137
• RFC 2763
• Floods the host names dynamically
• show isis topology shows the NSAPs getting dynamically mapped to the hostname
• Can turn it off using
[no] hostname dynamic
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Dynamic Host Name (Cont.)
• Always static CLNS host mappings have higher preference over dynamically learned mappings
• Static mappings can be seen with “show hosts” and dynamic mappings can be seen with “show isis hostname”
• If you remove the static CLNS host-name list on a router which is capable of dynamic-hostname exchange—we may not see this router itself in the ‘show isis hostname’ table immediately.
Rules
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Route Leaking
• RFC1195 defines all routers as STUB routers
• No information is leaked from routers in L2 into routers in L1
• Hence all L1-routers are forced to route to the closest L2-router
• This may result in sub-optimal routing
• This is IP only feature (CLNS still uses STUB)
464646NANOG24 © 2002, Cisco Systems, Inc. All rights reserved.
Route Leaking
• This new feature allows redistribution of L2-IP routes into L1 areas
• Enables Level 1-only routers to pick the best path to exit the area
• Enables shortest-exit and MED for BGP
• Enables MPLS-VPN (PE reachability) between areas
• Redistribution is controlled via distribute-lists
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Route Leaking
• Prefixes MUST be present in the routing table as ISIS level-2 routes
Otherwise no leaking occurs
Same criteria than L1 to L2
Inter-area routing is done through the routing table
484848NANOG24 © 2002, Cisco Systems, Inc. All rights reserved.
Route Leaking
• When leaking routes from L2 backbone into L1 areas a loop protection mechanism need to be used in order to prevent leaked routes to be re-injected into the backbone
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Route Leaking
L1L2
L1
L1L2 L1L2
L1L2L1
L1L2
L1
1. Level-1 LSP with IP prefix:10.14.0.0/16
4. At this point prefix 10.14.0.0/16 will NOT be inserted in L2 LSP since it has the Down-bit set
3. Level-1 LSP with IP prefix: 10.14.0.0/16 Up/Down-bit set
2. Level-2 LSP with IP prefix: 10.14.0.0/16
3. At this point prefix 10.14.0.0/16 will be inserted in L1 LSP since route leaking is configured AND the prefix is present in the routing table as a L2 route
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Route Leaking
L1L2
L1
L1L2
4. Level-2 LSP with IP prefix: 10.1.0.0/16
L1L2
L1L2 L1
L1L2
L11. Level-1 LSP withIP prefix: 10.1.0.0/16
2. Level-2 LSP with IP prefix: 10.1.0.0/16 2. Level-2 LSP with IP
prefix: 10.1.0.0/16
3. Level-1 LSP withIP prefix: 10.1.0.0/16Up/Down-Bit set
3. Level-2 LSP withIP prefix: 10.1.0.0/16
5. At this point the prefix 10.1.0.0/16 will NOT be inserted in the L1 LSP since a L1 route is preferred in the routing table
515151NANOG24 © 2002, Cisco Systems, Inc. All rights reserved.
Route Leaking
• TVLs 128 and 130 have a metric field that consists of 4 TOS metrics
The first metric, the so-called "default metric", has the high-order bit reserved (bit 8) Routers must set this bit to zero on transmission, and ignore it on receipt
• The high-order bit in the default metric field in TLVs 128 and 130 becomes the Up/Down bit
525252NANOG24 © 2002, Cisco Systems, Inc. All rights reserved.
Route Leaking
• RecommendationRecommendation: use wide Metric TLV (TLV 135)
• Configure with:
router isis metric-style wide
535353NANOG24 © 2002, Cisco Systems, Inc. All rights reserved.
Route Leaking (Cont.)
• Route leaking is implemented in both
12.0S and 12.1
Cisco IOS 12.0S command
advertise ip l2-into-l1 <100-199>
Cisco IOS 12.1 command
redistribute isis ip level-2 into level-1
distribute-list <100-199>
• Both commands are supported
545454NANOG24 © 2002, Cisco Systems, Inc. All rights reserved.
Route Leaking (Cont.)
• With this new change, when a user inputs older command (advertise ip), it will be changed to the newer syntax.
Router(config-router)#Router(config-router)#advertise ip l2-into-l1 100advertise ip l2-into-l1 100 advertise ip l2-into-l1 100advertise ip l2-into-l1 100 syntax will be converted intosyntax will be converted into redistribute isis ip level-2 into level-1 distribute-list 100redistribute isis ip level-2 into level-1 distribute-list 100
Commnad Allow Visible Write/NVRAMCommnad Allow Visible Write/NVRAM
OLD+NEW OLD+NEW NEWOLD+NEW OLD+NEW NEW
555555NANOG24 © 2002, Cisco Systems, Inc. All rights reserved.
Extensions for MPLS-TE
• New TLVs have been added for the support of MPLS-traffic engineering
• For reference they are:
Extended IS neighbor TLV # 22 (consists of Sub-TLVs)
Extended IP reachability TLV # 135
Router ID TLV # 134
• The IETF draft: draft-ietf-traffic-04.txtdraft-ietf-traffic-04.txt
565656NANOG24 © 2002, Cisco Systems, Inc. All rights reserved.
Extensions for MPLS-TE
Extended IS Reachability TLV # 22
# of Octets# of Octets
System-ID
Default Metric
Length of Sub-TLVs
66
11
33
11
Pseudonode ID
Optional Sub-TLVs 0-2440-244
575757NANOG24 © 2002, Cisco Systems, Inc. All rights reserved.
Extensions for MPLS-TE
Extended IS Reachability Sub-TLVs
Sub-TLV #Sub-TLV #
IPv4 Neighbor Address
Maximum Link Bandwidth
33
66
88
99
IPv4 Interface Address
Reservable Link Bandwidth 1010
Administrative Group (color)
Unreserved Bandwidth 11
TE Default Metric 18
585858NANOG24 © 2002, Cisco Systems, Inc. All rights reserved.
Extensions for MPLS-TE
Router ID TLV # 134• Useful as stable address for traffic engineering
# of Octets# of Octets
Router ID 44
595959NANOG24 © 2002, Cisco Systems, Inc. All rights reserved.
Extensions for MPLS-TE
Extended IP Reachability TLV # 135
# of Octets# of Octets
Metric
U/D Sub-TLV Prefix Length
IPv4 Prefix
Optional Sub-TLVs
44
11
44
0-2500-250
606060NANOG24 © 2002, Cisco Systems, Inc. All rights reserved.
Extensions for MPLS-TE
Extended IP Reachability Sub-TLV
Sub-TLV #Sub-TLV #
Administrative TAG11
616161NANOG24 © 2002, Cisco Systems, Inc. All rights reserved.
Fast Hellos
• Hold-time can be set to 1 second
interface POS0/0 isis hello-interval minimal
• By default hello-multiplier is 3
Hello packets sent every 333 msecs
626262NANOG24 © 2002, Cisco Systems, Inc. All rights reserved.
Fast Hellos (Cont.)
• AdvantagesReduced link failure detection time
• Disadvantages Increased BW/buffer/CPU usage can cause
missed hellos; potential increased adjacency
flapping can cause instability
Use no hello padding feature to reduce BW
and buffer usage
636363NANOG24 © 2002, Cisco Systems, Inc. All rights reserved.
dCEF and ISIS
• When CEF disabled on a LC, it should inform the Routing protocol.
• Since ISIS runs directly on top of L2, it still keeps the neighbor adjacency(ies) and doesn’t detect that the LC got disabled for the CEF.
• Hence black-holing of the traffic.
646464NANOG24 © 2002, Cisco Systems, Inc. All rights reserved.
dCEF and ISIS
• Under router-isis
external overload signallingexternal overload signalling
By default this option is disabled.By default this option is disabled.
[no][no] external overload signallingexternal overload signalling
Can be used as a workaround in case dCEF Can be used as a workaround in case dCEF
forgets to pass enable signal to ISIS forgets to pass enable signal to ISIS when dCEF is actually up. when dCEF is actually up.
656565NANOG24 © 2002, Cisco Systems, Inc. All rights reserved.
Route Tags
• The IP prefixes can be ‘tagged’ with Color/admin information.
• This may be useful to control the routes
redistributed between area/domain boundaries.
OR
• Can be used to apply for some policies to the
ISIS Routes.
• This is similar to what BGP is doing with the community attribute(s).
666666NANOG24 © 2002, Cisco Systems, Inc. All rights reserved.
Route Tags
10.1.1.0 /24
10.1.2.0 /24
L1
L1
L2
Rtr C doesn’t differentiate the IP Prefixes 10.1.1.0 vs 10.1.2.0
when it is leaking it to Rtr D if we wanted to have
some policy applied to these prefixes.
Rtr-A
Rtr-BRtr-C
Rtr-D
676767NANOG24 © 2002, Cisco Systems, Inc. All rights reserved.
Route Tags
• A New sub-TLV has been defined with a value
of 1 as a part of Extended IP Reachability TLV 135
• This admin-tag strings attached to the IP prefix are used to color the ISIS IP routes.
• The IETF Draft:
draft-martin-neal-policy-isis-admin-tags-02.txtdraft-martin-neal-policy-isis-admin-tags-02.txt
686868NANOG24 © 2002, Cisco Systems, Inc. All rights reserved.
Route Tags
• The ‘tag’ can be applied to:
an interface an interface
an external route(s)an external route(s)
while filtering between L1->L2 or L2->L1while filtering between L1->L2 or L2->L1
On Summary Addresses On Summary Addresses
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Route Tags
• The interface tagging is: isis tag X [X is between 1 & ]
• External-Routes tagging is: applied via route-map on a redistributed routes
[static etc]
• Filtering between L1->L2 or L2->L1 is: applied via route-map via redistribution option
• Summary Addresses summary-addresss [ip prefix, mask] tag [value] metic X
707070NANOG24 © 2002, Cisco Systems, Inc. All rights reserved.
Route Tags
• The current implementation supports only one tag value with the routes.
• The tag value can be seen via:
show isis database detail verboseshow isis database detail verbose
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P2P Adjacencies over Broadcast Media
• When Broadcast interfaces (Ethernet, FE, GE,
FDDI etc) used to connect only two routers,
tell IS-IS to behave as p2p: No Need for DIS Election
Also, no need for CSNPs
Reduce the number of nodes in SPT
(no Pseudonode)
• The IETF draft:
draft-ietf-isis-igp-p2p-over-lan-00.txtdraft-ietf-isis-igp-p2p-over-lan-00.txt
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P2P Adjacencies over Broadcast Media
RtrADIS
Rtr-BLAN topology
SPT topologyPseudonode
Rtr-A Rtr-B
• SPF doesn’t know anything about LANs
• All links are p2p
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P2P Adjacencies over Broadcast Media
LAN topology Rtr-A Rtr-B
Interface fa1/0 isis network point-to-point
SPT topologyRtr-A Rtr-B
• One step less in SPF computation
• No DIS election
• No CSNP flooding
•New CLI command under the interface:
[no] isis network point-to-point[no] isis network point-to-point
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MPLS-TEForwarding Adjacencies with IS-IS
• Ability to advertise the MPLS-TE Tunnels into the IGP (IS-IS) as a regular link.
• Then, IGP (IS-IS) will treat it as a normal link .
• This is called as “Forwarding Adjacencies”
• FA allows to mask the unequal physical topologies so that down-stream nodes can do load balancing to the destination node.
• This is a part of the draft:
draft-ietf-mpls-lsp-hierarchy-03.txt
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• Following are the caveats to remember: (wrt IS-IS)
LSP will be put into IS-IS Link State Database
IS-IS Hello will not run over the TE Tunnel
IS-IS LSPs wont’ be flooded over the TE Tunnels.
SPF bi-directional check will be enabled.
MPLS-TEForwarding Adjacencies with IS-IS
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MPLS-TEForwarding Adjacencies with IS-IS
Rtr-A
Rtr-B Rtr-CRtr-D
Rtr-E
Rtr-FRtr-G
10
10
10 10
MPLS-TE Tunnel
MPLS-TE Tunnel
10
10
10
With FA – RtrA & RtrE will know the MPLS-TE Tunnels as an additional link Allows load balancing on the un-equal cost paths. Hides the Core topology.
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MPLS-TE Forwarding Adjacencies with IS-IS
FA has the benefit in some particular
cases and is not recommended
everywhere.
We can not use FAs to do lsp-hierarchy
since there is no TE information on FAs
• 2 Points to Remember2 Points to Remember
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Suggested Reading
• ISO 10589 (IS-IS Intra-Domain Routing Exchange Protocol)
• RFC 1195 (OSI IS-IS for Routing in TCP/IP and Dual Environments)
• draft-ietf-isis-traffic-04.txt (TE Extensions for IS-IS)
• draft-ietf-isis-igp-p2p-over-lan-00.txt (P2P Adj over LAN)
• RFC 2966 (Route-leaking)
• RFC 2763 (Dynamic Hostname Exchange)
• draft-martin-neal-policy-isis-admin-tags-02.txt draft-martin-neal-policy-isis-admin-tags-02.txt (Route Tags)(Route Tags)
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