Monthly Archives: June 2015

Juniper BGP path selection

juniper
  1. Verify that the next hop can be resolved.
  2. Choose the path with the lowest preference value (routing protocol process preference).
  3. Prefer the path with higher local preference. For non-BGP paths, choose the path with the lowest preference2 value.
  4. If the accumulated interior gateway protocol (AIGP) attribute is enabled, prefer the path with the lower AIGP attribute.
  5. Prefer the path with the shortest autonomous system (AS) path value.
  6. Prefer the route with the lower origin code.  Routes learned from an IGP have a lower origin code than those learned from an exterior gateway protocol (EGP), and both have lower origin codes than incomplete routes (routes whose origin is unknown).
  7. Prefer the path with the lowest multiple exit discriminator (MED) metric.
  8. Prefer strictly internal paths, which include IGP routes and locally generated routes (static, direct, local, and so forth).
  9. Prefer strictly external BGP (EBGP) paths over external paths learned through internal BGP (IBGP) sessions.
  10. Prefer the path whose next hop is resolved through the IGP route with the lowest metric.
  11. If both paths are external, prefer the currently active path to minimize route-flapping.
  12. Prefer a primary route over a secondary route. A primary route is one that belongs to the routing table. A secondary route is one that is added to the routing table through an export policy.
  13. Prefer the path from the peer with the lowest router ID. For any path with an originator ID attribute, substitute the originator ID for the router ID during router ID comparison.
  14. Prefer the path with the shortest cluster list length. The length is 0 for no list.
  15. Prefer the path from the peer with the lowest peer IP address.

Cisco BGP path selection

cisco
  1. Prefer the path with the highest WEIGHT.  (Weight is a Cisco-proprietary attribute and is non-transitive)
  2. Prefer the path with the highest LOCAL_PREF.  (Default value is 100 and is non-transitive)
  3. Prefer the path that was locally originated via a network or aggregate BGP sub-command or through redistribution from an IGP.
  4. Prefer the path with the shortest AS_PATH.
  5. Prefer the path with the lowest origin type.
  6. Prefer the path with the lowest multi-exit discriminator (MED).
  7. Prefer eBGP over iBGP paths.
  8. Prefer the path with the lowest IGP metric to the BGP next hop.
  9. Determine if multiple paths require installation in the routing table for BGP Multipath.
  10. When both paths are external, prefer the path that was received first (the oldest one).
  11. Prefer the route that comes from the BGP router with the lowest router ID.
  12. If the originator or router ID is the same for multiple paths, prefer the path with the minimum cluster list length.
  13. Prefer the path that comes from the lowest neighbor address.

Comparing Cisco and Juniper administrative distance

cisco, juniper
Protocol Cisco Juniper
Connected / Direct 0 0
Static 1 5
EIGRP Summary 5 –
OSPF Internal – 10
IS-IS Level 1 Internal – 15
IS-IS Level 2 Internal – 18
BGP External 20 –
EIGRP Internal 90 –
OSPF All 110 –
IS-IS All 115 –
RIP 120 100
OSPF External – 150
IS-IS Level 1 External – 160
IS-IS Level 2 External – 165
EIGRP External 170 –
BGP All – 170
BGP Internal 200 –

IPv6 quick reference guide

ipv6
Prefix Bits IP Addresses /64s /48s In English
/64 64 18,446,744,073,709,551,616 1   18.446 Quintillion
/63 65 36,893,488,147,419,103,232 2   36.893 Quintillion
/62 66 73,786,976,294,838,206,464 4   73.786 Quintillion
/61 67 147,573,952,589,676,412,928 8   147.573 Quintillion
/60 68 295,147,905,179,352,825,856 16   295.147 Quintillion
/59 69 590,295,810,358,705,651,712 32   590.295 Quintillion
/58 70 1,180,591,620,717,411,303,424 64   1.180 Sextillion
/57 71 2,361,183,241,434,822,606,848 128   2.361 Sextillion
/56 72 4,722,366,482,869,645,213,696 256   4.722 Sextillion
/55 73 9,444,732,965,739,290,427,392 512   9.444 Sextillion
/54 74 18,889,465,931,478,580,854,784 1,024   18.889 Sextillion
/53 75 37,778,931,862,957,161,709,568 2,048   37.778 Sextillion
/52 76 75,557,863,725,914,323,419,136 4,096   75.557 Sextillion
/51 77 151,115,727,451,828,646,838,272 8,192   151.115 Sextillion
/50 78 302,231,454,903,657,293,676,544 16,384   302.231 Sextillion
/49 79 604,462,909,807,314,587,353,088 32,768   604.462 Sextillion
/48 80 1,208,925,819,614,629,174,706,176 65,536 1 1.208 Septillion
/47 81 2,417,851,639,229,258,349,412,352 131,072 2 2.417 Septillion
/46 82 4,835,703,278,458,516,698,824,704 262,144 4 4.835 Septillion
/45 83 9,671,406,556,917,033,397,649,408 524,288 8 9.671 Septillion
/44 84 19,342,813,113,834,066,795,298,816 1,048,576 16 19.342 Septillion
/43 85 38,685,626,227,668,133,590,597,632 2,097,152 32 38.685 Septillion
/42 86 77,371,252,455,336,267,181,195,264 4,194,304 64 77.371 Septillion
/41 87 154,742,504,910,672,534,362,390,528 8,388,608 128 154.742 Septillion
/40 88 309,485,009,821,345,068,724,781,056 16,777,216 256 309.485 Septillion
/39 89 618,970,019,642,690,137,449,562,112 33,554,432 512 618.970 Septillion
/38 90 1,237,940,039,285,380,274,899,124,224 67,108,864 1,024 1.237 Octillion
/37 91 2,475,880,078,570,760,549,798,248,448 134,217,728 2,048 2.475 Octillion
/36 92 4,951,760,157,141,521,099,596,496,896 268,435,456 4,096 4.951 Octillion
/35 93 9,903,520,314,283,042,199,192,993,792 536,870,912 8,192 9.903 Octillion
/34 94 19,807,040,628,566,084,398,385,987,584 1,073,741,824 16,384 19.807 Octillion
/33 95 39,614,081,257,132,168,796,771,975,168 2,147,483,648 32,768 39.614 Octillion
/32 96 79,228,162,514,264,337,593,543,950,336 4,294,967,296 65,536 79.228 Octillion
/31 97 158,456,325,028,528,675,187,087,900,672 8,589,934,592 131,072 158.456 Octillion
/30 98 316,912,650,057,057,350,374,175,801,344 17,179,869,184 262,144 316.912 Octillion
/29 99 633,825,300,114,114,700,748,351,602,688 34,359,738,368 524,288 633.825 Octillion
/28 100 1,267,650,600,228,229,401,496,703,205,376 68,719,476,736 1,048,576 1.267 Nonillion
/27 101 2,535,301,200,456,458,802,993,406,410,752 137,438,953,472 2,097,152 2.535 Nonillion
/26 102 5,070,602,400,912,917,605,986,812,821,504 274,877,906,944 4,194,304 5.070 Nonillion
/25 103 10,141,204,801,825,835,211,973,625,643,008 549,755,813,888 8,388,608 10.141 Nonillion
/24 104 20,282,409,603,651,670,423,947,251,286,016 1,099,511,627,776 16,777,216 20.282 Nonillion

IPv4 quick reference

ipv4
Prefix Bits IP Addresses /24s /16s /8s Subnet Mask
/32 0 1       255.255.255.255
/31 1 2       255.255.255.254
/30 2 4       255.255.255.252
/29 3 8       255.255.255.248
/28 4 16       255.255.255.240
/27 5 32       255.255.255.224
/26 6 64       255.255.255.192
/25 7 128       255.255.255.128
/24 8 256 1     255.255.255.0
/23 9 512 2     255.255.254.0
/22 10 1,024 4     255.255.252.0
/21 11 2,048 8     255.255.248.0
/20 12 4,096 16     255.255.240.0
/19 13 8,192 32     255.255.224.0
/18 14 16,384 64     255.255.192.0
/17 15 32,768 128     255.255.128.0
/16 16 65,536 256 1   255.255.0.0
/15 17 131,072 512 2   255.254.0.0
/14 18 262,144 1,024 4   255.252.0.0
/13 19 524,288 2,048 8   255.248.0.0
/12 20 1,048,576 4,096 16   255.240.0.0
/11 21 2,097,152 8,192 32   255.224.0.0
/10 22 4,194,304 16,384 64   255.192.0.0
/9 23 8,388,608 32,768 128   255.128.0.0
/8 24 16,777,216 65,536 256 1 255.0.0.0
/7 25 33,554,432 131,072 512 2 254.0.0.0
/6 26 67,108,864 262,144 1,024 4 252.0.0.0
/5 27 134,217,728 524,288 2,048 8 248.0.0.0
/4 28 268,435,456 1,048,576 4,096 16 240.0.0.0
/3 29 536,870,912 2,097,152 8,192 32 224.0.0.0
/2 30 1,073,741,824 4,194,304 16,384 64 192.0.0.0
/1 31 2,147,483,648 8,388,608 32,768 128 128.0.0.0
/0 32 4,294,967,296 16,777,216 65,536 256 0.0.0.0