ECMP Handling When IP Route Sharing Is Disabled

If IP route sharing is disabled, the first best route is installed in the hardware table, if multiple best routes are available. Hence the compression algorithm considers the first best route for ECMP cases. As shown in the following table, when IP route sharing is disabled, all routes are compressed, except the first one in this case.

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Route Manager‘s Table When IP Route Sharing is Disabled

Prefix Gateways Compressed?
20.0.0.0/8 Gw1: 30.1.10.1, Gw2: 50.1.10.1 NO
20.1.10.0/24 Gw1: 30.1.10.1 YES
20.2.10.0/24 Gw1: 30.1.10.1, Gw2: 60.1.10.1 YES
20.3.10.0/24 Gw1: 30.1.10.1, Gw2: 50.1.10.1 YES
20.4.10.0/24 Gw1: 30.1.10.1, Gw2: 50.1.10.1 Gw3: 60.1.10.1 YES
20.1.10.44/32 Gw1: 30.1.10.1 Gw2: 50.1.10.1 YES
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HAL(TCAM)/Kernel Routing Table When IP Route Sharing is Disabled

Prefix Gateway
20.0.0.8/16 Gw1: 30.1.10.1,

Sample output is shown below:

* (debug) # disable iproute sharing
* (debug) # show iproute
Ori Destination        Gateway         Mtr  Flags        VLAN       Duration
#s  Default Route      12.1.10.10      1    UG---S-um--f v1         0d:19h:58m:58s
#s  Default Route      12.1.10.12      1    UG---S-um--- v1         0d:19h:12m:53s
#d  12.1.10.0/24       12.1.10.62      1    U------um--f v1         0d:19h:58m:59s
d  16.1.10.0/24       16.1.10.62      1    -------um--- v16        0d:19h:58m:59s
#d  22.1.10.0/24       22.1.10.62      1    U------um--f v2         0d:19h:58m:59s
#s  33.33.33.0/24      12.1.10.25      1    UG---S-um--f v1         0d:19h:58m:58s
#s  55.0.0.0/8         12.1.10.10      1    UG---S-um--c v1         0d:19h:58m:58s
#s  55.0.0.0/8         22.1.10.33      1    UG---S-um--- v2         0d:19h:58m:58s
#s  55.2.1.1/32        12.1.10.22      1    UG---S-um--f v1         0d:19h:58m:58s
#s  55.5.5.1/32        12.1.10.44      1    UG---S-um--f v1         0d:19h:58m:58s
#s  66.0.0.0/8         12.1.10.12      1    UG---S-um--f v1         0d:19h:58m:58s
#s  66.0.0.0/16        12.1.10.12      1    UG---S-um--c v1         0d:19h:58m:58s
#d  70.1.10.0/24       70.1.10.62      1    U------um--f v7         0d:19h:58m:59s
#s  78.0.0.0/8         12.1.10.10      1    UG---S-um--c v1         0d:19h:58m:58s
#s  79.0.0.0/8         12.1.10.10      1    UG---S-um--c v1         0d:19h:58m:58s
#s  79.0.0.0/8         12.1.10.12      1    UG---S-um--- v1         0d:19h:58m:58s
#s  80.0.0.0/8         12.1.10.10      1    UG---S-um--c v1         0d:19h:58m:58s
#d  80.1.10.0/24       80.1.10.62      1    U------um--f v8         0d:19h:58m:59s
#s  81.0.0.0/8         12.1.10.10      1    UG---S-um--c v1         0d:19h:58m:58s
#s  81.0.0.0/8         12.1.10.12      1    UG---S-um--- v1         0d:19h:58m:58s
#s  81.0.0.0/8         12.1.10.13      1    UG---S-um--- v1         0d:19h:58m:58s
#s  82.0.0.0/8         12.1.10.10      1    UG---S-um--c v1         0d:19h:58m:58s
#s  83.0.0.0/8         12.1.10.10      1    UG---S-um--c v1         0d:19h:58m:58s
#d  91.1.10.0/24       91.1.10.62      1    U------um--f v9         0d:19h:58m:59s
#d  92.1.10.0/24       92.1.10.62      1    U------um--f v10        0d:19h:59m:2s
#d  93.1.10.0/24       93.1.10.62      1    U------um--f v11        0d:19h:59m:2s

Origin(Ori): (b) BlackHole, (be) EBGP, (bg) BGP, (bi) IBGP, (bo) BOOTP
(ct) CBT, (d) Direct, (df) DownIF, (dv) DVMRP, (e1) ISISL1Ext
(e2) ISISL2Ext, (h) Hardcoded, (i) ICMP, (i1) ISISL1 (i2) ISISL2
(is) ISIS, (mb) MBGP, (mbe) MBGPExt, (mbi) MBGPInter, (mp) MPLS Lsp
(mo) MOSPF (o) OSPF, (o1) OSPFExt1, (o2) OSPFExt2
(oa) OSPFIntra, (oe) OSPFAsExt, (or) OSPFInter, (pd) PIM-DM, (ps) PIM-SM
(r) RIP, (ra) RtAdvrt, (s) Static, (sv) SLB_VIP, (un) UnKnown
(*) Preferred unicast route (@) Preferred multicast route
(#) Preferred unicast and multicast route

Flags: (B) BlackHole, (D) Dynamic, (G) Gateway, (H) Host Route
(L) Matching LDP LSP, (l) Calculated LDP LSP, (m) Multicast
(P) LPM-routing, (R) Modified, (S) Static, (s) Static LSP
(T) Matching RSVP-TE LSP, (t) Calculated RSVP-TE LSP, (u) Unicast, (U) Up
(f) Provided to FIB (c) Compressed Route

Mask distribution:
2 default routes               12 routes at length 8
1 routes at length 16           9 routes at length 24
2 routes at length 32
Route Origin distribution:
8 routes from Direct              18 routes from Static

Total number of routes = 26
Total number of compressed routes = 8

LSP Route Handling

An LSP route is compressed only in the following circumstances:
  • If the parent node of the LSP route is also an LSP route

  • If the LSP nexthop of the parent node matches with this node