1 © 2000, Cisco Systems, Inc. Integrated-ISIS Route Leaking.
-
Upload
tommy-sharick -
Category
Documents
-
view
220 -
download
0
Transcript of 1 © 2000, Cisco Systems, Inc. Integrated-ISIS Route Leaking.
2© 2000, Cisco Systems, Inc.
ISIS routing LevelsISIS routing Levels
L1
L1L2
L1
L1L2L12. Level-1 LSP withIP prefix: 10.1.0.0/16
2. Level-1 LSP withIP prefix: 10.10.0.0/16
L1
1. Level-1 LSP withAttached-bit (used as a default route by all level-1routers
3. Level-2 LSP withIP prefix: 10.1.0.0/16IP prefix: 10.10.0.0/16
Routers within an area do not have any routing information about prefixes originated outside the area. Default routing (ATT-bit or explicit 0.0.0.0/0) is used to reach destinations outside the area.
3© 2000, Cisco Systems, Inc.
ISIS routing LevelsISIS routing Levels
L1L2
L1
L2L2
L1L2L1
L1L2
L11. Level-1 LSP withIP prefix: 10.1.0.0/16
4. At this point the prefix 10.1.0.0/16 will NOT be inserted in the L1 LSP (no route leaking by default)
2. Level-2 LSP withIP prefix: 10.1.0.0/16 2. Level-2 LSP with
IP prefix: 10.1.0.0/16
3. Level-2 LSP withIP prefix: 10.1.0.0/16
3. Level-2 LSP withIP prefix: 10.1.0.0/16
2. At this point prefix 10.1.0.0/16 will be inserted in L2 LSP
2. At this point prefix 10.1.0.0/16 is inserted in L2 LSP
0. Level-1 LSP with ATT bit set
0. Level-1 LSP with ATT bit set
0. Level-1 LSP with ATT bit set
4© 2000, Cisco Systems, Inc.
Route LeakingRoute 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 LeakingRoute Leaking
L1L2
L1
L1L2L1L2
L1L2L1
L1L2
L1
1. Level-1 LSP withIP 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
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
2. Level-2 LSP withIP prefix: 10.14.0.0/16
6© 2000, Cisco Systems, Inc.
Route LeakingRoute Leaking
L1L2
L1
L1L2
4. Level-2 LSP withIP prefix: 10.1.0.0/16
L1L2
L1L2L1
L1L2
L11. Level-1 LSP withIP prefix: 10.1.0.0/16
2. Level-2 LSP withIP prefix: 10.1.0.0/16 2. Level-2 LSP with
IP 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
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
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
7© 2000, Cisco Systems, Inc.
Route LeakingRoute 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 LeakingRoute 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 LeakingRoute 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 LeakingRoute 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 LeakingRoute 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 LeakingRoute 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 LeakingRoute 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 LeakingRoute Leaking
• 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
• 12.0S command will be converted into 12.1 syntax
15© 2000, Cisco Systems, Inc.
Route Leaking A bit of bits history
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
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 LeakingRoute Leaking
R2
R3-12.1
2. Level-2 LSP with IP prefix: 10.1.0.0/16
2. At this point R3 (12.1) will NOT insert 10.4.0.0/16 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 withIP prefix: 10.4.0.0/16Bit-8 is set
1. Level-1 LSP withIP prefix: 10.1.0.0/16
• 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 LeakingRoute Leaking
R2
R3
6. LOOP !!!4. R1 (12.0S) Advertises the prefix back to level-2 since itdoesn’t understand the Down-bit
1. Level-1 LSP withIP prefix: 10.4.0.0/16
• 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 withIP prefix: 10.4.0.0/16Down-bit Set (bit-8)
2. Level-2 LSP withIP prefix: 10.4.0.0/16
5. Level-2 LSP withIP prefix: 10.4.0.0/16
19© 2000, Cisco Systems, Inc.
Always use TLV-135 Always use TLV-135 Configure routers with:Configure routers with:
Router isisRouter isis metric-style wide metric-style wide
Route Leaking Recommendation
Route Leaking Recommendation
Don’t use Don’t use ““metric-type external”metric-type external”
when redistributing into ISISwhen redistributing into ISIS