1 © 2000, Cisco Systems, Inc. Integrated-ISIS Route Leaking

2 © 2000, Cisco Systems, Inc. ISIS routing Levels L1L1L2L1L1L2L1 2. Level-1 LSP with IP prefix: /16 2. Level-1 LSP with IP prefix: /16 L1 1. Level-1 LSP with Attached-bit (used as a default route by all level-1routers 3. Level-2 LSP with IP prefix: /16 IP prefix: /16 Routers within an area do not have any routing information about prefixes originated outside the area. Default routing (ATT-bit or explicit /0) is used to reach destinations outside the area.

3 © 2000, Cisco Systems, Inc. ISIS routing Levels L1L2L1 L2 L1L2L1L1L2L1 1. Level-1 LSP with IP prefix: /16 4. At this point the prefix /16 will NOT be inserted in the L1 LSP (no route leaking by default) 2. Level-2 LSP with IP prefix: /16 3. Level-2 LSP with IP prefix: /16 2. At this point prefix /16 will be inserted in L2 LSP 2. At this point prefix /16 is inserted in L2 LSP 0. Level-1 LSP with ATT bit set

4 © 2000, Cisco Systems, Inc. Route Leaking New ISIS feature/capability described in draft-ietf-isis-domain-wide Allows L1L2 routers to insert in their L1 LSP IP prefixes learned from L2 database if also present in the routing table ISIS areas are not stubby anymore

5 © 2000, Cisco Systems, Inc. Route Leaking L1L2L1 L1L2 L1L1L2L1 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 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 2. Level-2 LSP with IP prefix: /16

6 © 2000, Cisco Systems, Inc. Route Leaking L1L2L1 L1L2 4. Level-2 LSP with IP prefix: /16 L1L2 L1L1L2L1 1. Level-1 LSP with IP prefix: /16 2. 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 3. Level-1 LSP with IP prefix: /16 Up/Down-Bit set 3. Level-2 LSP with IP prefix: /16

7 © 2000, Cisco Systems, Inc. Route Leaking For IP only Prefixes MUST be present in the routing table as ISIS level-2 routes Otherwise no leaking occurs Same criteria as L1 ---> L2 Inter-area routing is done through the routing table

8 © 2000, Cisco Systems, Inc. Route Leaking Solution for several issues: optimal inter-area routing BGP shortest path to AS exit point MPLS-VPN (PEs loopback reachability)

9 © 2000, Cisco Systems, Inc. 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

10 © 2000, Cisco Systems, Inc. Route Leaking UP/Down bit Extended IP Reachability TLV (135) contains Up/Down bit Described in draft-ietf-isis-traffic UP/Down bit is set each time a prefix is leaked into a lower level Allows multi-level hierarchy route leaking Prefixes with Up/Down bit set are NEVER propagated to a upper level

11 © 2000, Cisco Systems, Inc. Route Leaking Route leaking works also with IP Internal Reachability Information (TLV 128) IP External Reachability Information (TLV 130) Also known as: Old-style or Narrow-metric TLVs

12 © 2000, Cisco Systems, Inc. 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

13 © 2000, Cisco Systems, Inc. Route Leaking Route leaking can be used with both: IP reachability TLVs: 128 and 130 Default Metric Bit-8 is used as Up/Down bit Extended IP Reachability TLV: 135 Up/Down bit

14 © 2000, Cisco Systems, Inc. Route Leaking 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 12.0S command will be converted into 12.1 syntax

15 © 2000, Cisco Systems, Inc. Route Leaking A bit of bits history 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 Bit 7 indicates the metric type (internal or external), and may be set to zero indicating internal metrics, or may be set to 1 indicating external metrics (only in TLV130)

16 © 2000, Cisco Systems, Inc. Route Leaking A bit of bits history However……………. Cisco IOS software BEFORE 12.1 uses bit 8 as I/E bit !!!! Since VERY early stage of ISIS implementation When doing (under “router isis”) redistribute …. metric-type external !!!!! bit 8 is set instead of bit 7 !!!!!!!

17 © 2000, Cisco Systems, Inc. Route Leaking R2 R Level-2 LSP with IP prefix: /16 2. At this point R3 (12.1) will NOT insert /16 in its L2 LSP since it considered the Up/Down bit set R1-12.0S 1. R1 (12.0S) redistributes into ISIS with “metric-type external” Therefore bit-8 is (wrongly) set 1. Level-1 LSP with IP prefix: /16 Bit-8 is set 1. Level-1 LSP with IP prefix: /16 L1L2 router using Cisco IOS from 12.1 will NOT put in L2 LSP any prefix with Up/Down bit set Even if route leaking is not configured Up/Down bit for TLVs 128, 130 and 135

18 © 2000, Cisco Systems, Inc. Route Leaking R2 R3 6. LOOP !!! 4. R1 (12.0S) Advertises the prefix back to level-2 since it doesn’t understand the Down-bit 1. Level-1 LSP with IP prefix: /16 L1L2 router using Cisco IOS 12.0S will put in L2 LSP any TLV128 or TLV130 prefix since Up/Down bit is not recognized Even if route leaking is not configured R1-12.0S 3. Level-1 LSP with IP prefix: /16 Down-bit Set (bit-8) 2. Level-2 LSP with IP prefix: /16 5. Level-2 LSP with IP prefix: /16

19 © 2000, Cisco Systems, Inc. Always use TLV-135 Configure routers with: Router isis metric-style wide Router isis metric-style wide Route Leaking Recommendation Don’t use “metric-type external” when redistributing into ISIS