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1 NANAOG24 © 2001, Cisco Systems, Inc. All rights reserved. © 2002, Cisco Systems, Inc. All rights reserved. IS-IS Deployment, Design Guidelines and New.

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Presentation on theme: "1 NANAOG24 © 2001, Cisco Systems, Inc. All rights reserved. © 2002, Cisco Systems, Inc. All rights reserved. IS-IS Deployment, Design Guidelines and New."— Presentation transcript:

1 1 NANAOG24 © 2001, Cisco Systems, Inc. All rights reserved. © 2002, Cisco Systems, Inc. All rights reserved. IS-IS Deployment, Design Guidelines and New Features Shankar Vemulapalli Internet Engineering Support

2 222 NANOG24 © 2002, Cisco Systems, Inc. All rights reserved. Agenda Scope of the Presentation Deployment Scenarios L1-Only L2-Only L1 & L2 With Route Leaking Design Considerations Set Over Load Bit LSP Flooding SPF PRC LSP Generation and MORE New Features Route Leaking Route Tags Extensions to MPLS-TE and MORE

3 333 NANOG24 © 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.

4 444 NANOG24 © 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).

5 5 NANAOG24 © 2001, Cisco Systems, Inc. All rights reserved. © 2002, Cisco Systems, Inc. All rights reserved. Deployment Scenarios

6 666 NANOG24 © 2002, Cisco Systems, Inc. All rights reserved. L1-Only POPs POP 1 L1-Only POP 3 L1-Only CORE L1-Only POP 4 L1-Only POP 2 L1-Only

7 777 NANOG24 © 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

8 888 NANOG24 © 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

9 999 NANOG24 © 2002, Cisco Systems, Inc. All rights reserved. L2-Only POPs (all in the same area) POP 1 Area POP 3 Area POP 2 Area CORE L2-Only POP 4 Area

10 10 NANOG24 © 2002, Cisco Systems, Inc. All rights reserved. L2-Only POPs (Each POP in a different area) POP 1 Area POP 3 Area POP 2 Area CORE L2-ONLY POP 4 Area

11 11 NANOG24 © 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 +/ 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

12 12 NANOG24 © 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 [ | wait-for-bgp] ]  max-lsp-lifetime  isp-refresh-interval  spf-interval 10  prc-interval  metric-style wide  [no] hello-padding [either turned globally or per-interface basis]  log-adjacency-changes  ignore-lsp-errors

13 13 NANOG24 © 2002, Cisco Systems, Inc. All rights reserved. L1 in the POP and L2 in the Core POP 1 L1-Only Area POP 3 L1-Only Area POP 2 L1-Only Area CORE L2-Only Area POP 4 L1-Only Area L1L2

14 14 NANOG24 © 2002, Cisco Systems, Inc. All rights reserved. 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.

15 15 NANOG24 © 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

16 16 NANAOG24 © 2001, Cisco Systems, Inc. All rights reserved. © 2002, Cisco Systems, Inc. All rights reserved. Design Considerations

17 17 NANOG24 © 2002, Cisco Systems, Inc. All rights reserved. Set Over Load Bit 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

18 18 NANOG24 © 2002, Cisco Systems, Inc. All rights reserved. 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-1 Rtr-2 Rtr-3 Rtr-4 Rtr-5

19 19 NANOG24 © 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

20 20 NANOG24 © 2002, Cisco Systems, Inc. All rights reserved. Set Over Load Bit (Cont.) router isis set-overload-bit set-overload-bit on-startup set-overload-bit on-startup wait-for-bgp router bgp 100 bgp update-delay

21 21 NANOG24 © 2002, Cisco Systems, Inc. All rights reserved. Set Over Load Bit (Cont.) Enhanced configuration: router isis set-overload-bit [on-startup[ |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.

22 22 NANOG24 © 2002, Cisco Systems, Inc. All rights reserved. LSP Flooding ISO 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

23 23 NANOG24 © 2002, Cisco Systems, Inc. All rights reserved. LSP Flooding (Cont.) Time between flooding consecutive LSP’s is configurable: Rtr-A(config)#int serial0 Rtr-A(config-if)#isis lsp-interval? 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

24 24 NANOG24 © 2002, Cisco Systems, Inc. All rights reserved. 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

25 25 NANOG24 © 2002, Cisco Systems, Inc. All rights reserved. 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

26 26 NANOG24 © 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

27 27 NANOG24 © 2002, Cisco Systems, Inc. All rights reserved. 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.

28 28 NANOG24 © 2002, Cisco Systems, Inc. All rights reserved. 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…

29 29 NANOG24 © 2002, Cisco Systems, Inc. All rights reserved. Exponential Backoff: Enhancements to SPF Algorithms SPF Incremental-Interval Initial-Wait 5.5 Sec Maximum-Interval 10 Sec PRC 5 Sec 2 Sec 5 Sec LSP Generation LSP Generation 5 Sec 50 msec 5 Sec

30 30 NANOG24 © 2002, Cisco Systems, Inc. All rights reserved. Exponential Backoff: spf-interval Extended syntax spf-interval [ ] seconds between consecutive SPF runs(seconds) initial wait before the first SPF (msecs) minimum wait between first and second SPF (msecs)

31 31 NANOG24 © 2002, Cisco Systems, Inc. All rights reserved. Exponential Backoff: spf-interval Example spf-interval (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

32 32 NANOG24 © 2002, Cisco Systems, Inc. All rights reserved. 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)

33 33 NANOG24 © 2002, Cisco Systems, Inc. All rights reserved. Exponential Backoff: prc-interval and lsp-gen-interval Same Syntax for  prc-interval  lsp-gen-interval

34 34 NANOG24 © 2002, Cisco Systems, Inc. All rights reserved. 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

35 35 NANOG24 © 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

36 36 NANOG24 © 2002, Cisco Systems, Inc. All rights reserved. Timer Default Value Cisco IOS Command Maxage LSP Refresh Interval LSP Transmission Interval LSP Retransmit Interval CSNP Interval 1200s 900s 33ms 5s 10s isis max-lsp-Interval isis refresh-interval isis lsp-interval isis retransmit-interval isis csnp-interval Database Timers

37 37 NANOG24 © 2002, Cisco Systems, Inc. All rights reserved. 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.

38 38 NANOG24 © 2002, Cisco Systems, Inc. All rights reserved. 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)

39 39 NANOG24 © 2002, Cisco Systems, Inc. All rights reserved. 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

40 40 NANOG24 © 2002, Cisco Systems, Inc. All rights reserved. Non-Advertisement of Parallel Adjacencies in the LSP (Cont.) LSP A IS: 5 B IS: 3 B IS: 3 C IS: 5 D LSP B IS: 5 A IS: 3 A IS: 6 C IS: 2 D Only the best Parallel Adjacency is reported Rtr-BRtr-A Rtr-C Rtr-D

41 41 NANAOG24 © 2001, Cisco Systems, Inc. All rights reserved. © 2002, Cisco Systems, Inc. All rights reserved. New Features

42 42 NANOG24 © 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

43 43 NANOG24 © 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

44 44 NANOG24 © 2002, Cisco Systems, Inc. All rights reserved. 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

45 45 NANOG24 © 2002, Cisco Systems, Inc. All rights reserved. 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)

46 46 NANOG24 © 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

47 47 NANOG24 © 2002, Cisco Systems, Inc. All rights reserved. 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

48 48 NANOG24 © 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

49 49 NANOG24 © 2002, Cisco Systems, Inc. All rights reserved. Route Leaking L1L2 L1 L1L2 L1 L1L2 L1 1. Level-1 LSP with IP prefix: /16 4. At this point prefix /16 will NOT be inserted in L2 LSP since it has the Down-bit set 3. Level-1 LSP with IP prefix: /16 Up/Down-bit set 2. Level-2 LSP with IP prefix: /16 3. At this point prefix /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

50 50 NANOG24 © 2002, Cisco Systems, Inc. All rights reserved. Route Leaking L1L2 L1 L1L2 4. Level-2 LSP with IP prefix: /16 L1L2 L1 L1L2 L1 1. Level-1 LSP with IP prefix: /16 2. Level-2 LSP with IP prefix: /16 3. Level-1 LSP with IP prefix: /16 Up/Down-Bit set 3. Level-2 LSP with IP prefix: /16 5. At this point the prefix /16 will NOT be inserted in the L1 LSP since a L1 route is preferred in the routing table

51 51 NANOG24 © 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

52 52 NANOG24 © 2002, Cisco Systems, Inc. All rights reserved. Route Leaking RecommendationRecommendation: use wide Metric TLV (TLV 135) Configure with: router isis metric-style wide

53 53 NANOG24 © 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 Cisco IOS 12.1 command redistribute isis ip level-2 into level-1 distribute-list Both commands are supported

54 54 NANOG24 © 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)#advertise ip l2-into-l1 100 Router(config-router)#advertise ip l2-into-l1 100 advertise ip l2-into-l1 100 advertise ip l2-into-l1 100 syntax will be converted into syntax will be converted into redistribute isis ip level-2 into level-1 distribute-list 100 redistribute isis ip level-2 into level-1 distribute-list 100 Commnad Allow Visible Write/NVRAM OLD+NEW OLD+NEW NEW OLD+NEW OLD+NEW NEW

55 55 NANOG24 © 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 draft-ietf-traffic-04.txtThe IETF draft: draft-ietf-traffic-04.txt

56 56 NANOG24 © 2002, Cisco Systems, Inc. All rights reserved. Extensions for MPLS-TE Extended IS Reachability TLV # 22 # of Octets System-ID Default Metric Length of Sub-TLVs Pseudonode ID Optional Sub-TLVs 0-244

57 57 NANOG24 © 2002, Cisco Systems, Inc. All rights reserved. Extensions for MPLS-TE Extended IS Reachability Sub-TLVs Sub-TLV # IPv4 Neighbor Address Maximum Link Bandwidth IPv4 Interface Address Reservable Link Bandwidth 10 Administrative Group (color) Unreserved Bandwidth 11 TE Default Metric 18

58 58 NANOG24 © 2002, Cisco Systems, Inc. All rights reserved. Extensions for MPLS-TE Router ID TLV # 134 Useful as stable address for traffic engineering # of Octets Router ID 4 4

59 59 NANOG24 © 2002, Cisco Systems, Inc. All rights reserved. Extensions for MPLS-TE Extended IP Reachability TLV # 135 # of Octets Metric U/DSub-TLVPrefix Length IPv4 Prefix Optional Sub-TLVs

60 60 NANOG24 © 2002, Cisco Systems, Inc. All rights reserved. Extensions for MPLS-TE Extended IP Reachability Sub-TLV Sub-TLV # Administrative TAG 1 1

61 61 NANOG24 © 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

62 62 NANOG24 © 2002, Cisco Systems, Inc. All rights reserved. Fast Hellos (Cont.) Advantages Reduced 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

63 63 NANOG24 © 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.

64 64 NANOG24 © 2002, Cisco Systems, Inc. All rights reserved. dCEF and ISIS Under router-isis external overload signalling By default this option is disabled. By default this option is disabled. [no]external overload signalling [no] external overload signalling Can be used as a workaround in case dCEF forgets to pass enable signal to ISIS when dCEF is actually up.

65 65 NANOG24 © 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).

66 66 NANOG24 © 2002, Cisco Systems, Inc. All rights reserved. Route Tags / /24 L1 L2 Rtr C doesn’t differentiate the IP Prefixes vs when it is leaking it to Rtr D if we wanted to have some policy applied to these prefixes. Rtr-A Rtr-B Rtr-C Rtr-D

67 67 NANOG24 © 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.txt

68 68 NANOG24 © 2002, Cisco Systems, Inc. All rights reserved. Route Tags The ‘tag’ can be applied to: an interface  an interface  an external route(s)  while filtering between L1->L2 or L2->L1  On Summary Addresses

69 69 NANOG24 © 2002, Cisco Systems, Inc. All rights reserved. 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

70 70 NANOG24 © 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 verbose show isis database detail verbose

71 71 NANOG24 © 2002, Cisco Systems, Inc. All rights reserved. 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.txt draft-ietf-isis-igp-p2p-over-lan-00.txt

72 72 NANOG24 © 2002, Cisco Systems, Inc. All rights reserved. P2P Adjacencies over Broadcast Media RtrA DIS Rtr-B LAN topology SPT topology Pseudonode Rtr-A Rtr-B SPF doesn’t know anything about LANs All links are p2p

73 73 NANOG24 © 2002, Cisco Systems, Inc. All rights reserved. P2P Adjacencies over Broadcast Media LAN topology Rtr-A Rtr-B Interface fa1/0 isis network point-to-point SPT topology Rtr-ARtr-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

74 74 NANOG24 © 2002, Cisco Systems, Inc. All rights reserved. MPLS-TE Forwarding 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

75 75 NANOG24 © 2002, Cisco Systems, Inc. All rights reserved. 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-TE Forwarding Adjacencies with IS-IS

76 76 NANOG24 © 2002, Cisco Systems, Inc. All rights reserved. MPLS-TE Forwarding Adjacencies with IS-IS Rtr-A Rtr-B Rtr-C Rtr-D Rtr-E Rtr-FRtr-G 10 MPLS-TE Tunnel 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.

77 77 NANOG24 © 2002, Cisco Systems, Inc. All rights reserved. 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 Remember 2 Points to Remember

78 78 NANOG24 © 2002, Cisco Systems, Inc. All rights reserved. Suggested Reading ISO (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 (Route Tags)draft-martin-neal-policy-isis-admin-tags-02.txt (Route Tags)

79 79 RST _05_2001_c1 © 2001, Cisco Systems, Inc. All rights reserved.


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