Dell PowerConnect M6220 Configuration Guide - Page 81

Using Equal Cost Multipath, Example 2: Assigning Administrative Preferences to Static Routes

Get Dell PowerConnect M6220 PDF manuals and user guides View all Dell PowerConnect M6220 manuals
Add to My Manuals
Save this manual to your list of manuals

Page 81 highlights

Example 2: Assigning Administrative Preferences to Static Routes By default, static routes are assigned a preference value of 1. The following command changes this default: console#Config ip route distance 20 exit When you configure a static route, you can assign a preference value to it. The preference overrides the setting inherited as the default value for static routes. In this example, two static routes are defined to the same destination but with different next hops and different preferences (25 and 30). The route with the higher preference will only be used when the preferred route is unavailable: console#Config ip route 10.25.67.0 255.255.255.0 10.25.22.2 metric 25 ip route 10.25.67.0 255.255.255.0 10.25.21.0 metric 30 exit Similarly, you can create two default routes-one preferred and the other used as a backup. In this example, the preference values 1 and 10 are assigned: console#Config ip route default 10.25.67.2 1 ip route default 10.25.67.7 10 exit Using Equal Cost Multipath The equal cost multipath (ECMP) feature allows a router to use more than one next hop to forward packets to a given destination prefix. It can be used to promote a more optimal use of network resources and bandwidth. A router that does not use ECMP forwards all packets to a given destination through a single next hop. This next hop may be chosen from among several next hops that provide equally good routes to the destination. For example, in Figure 4-7, Router A sends all traffic to destinations in Network D through next hop NH1, even though the route through NH2 is equally good. Forwarding all traffic via NH1 may cause Link A to be overloaded while Link B is not used at all. Routing Configuration 81

  • 1
  • 2
  • 3
  • 4
  • 5
  • 6
  • 7
  • 8
  • 9
  • 10
  • 11
  • 12
  • 13
  • 14
  • 15
  • 16
  • 17
  • 18
  • 19
  • 20
  • 21
  • 22
  • 23
  • 24
  • 25
  • 26
  • 27
  • 28
  • 29
  • 30
  • 31
  • 32
  • 33
  • 34
  • 35
  • 36
  • 37
  • 38
  • 39
  • 40
  • 41
  • 42
  • 43
  • 44
  • 45
  • 46
  • 47
  • 48
  • 49
  • 50
  • 51
  • 52
  • 53
  • 54
  • 55
  • 56
  • 57
  • 58
  • 59
  • 60
  • 61
  • 62
  • 63
  • 64
  • 65
  • 66
  • 67
  • 68
  • 69
  • 70
  • 71
  • 72
  • 73
  • 74
  • 75
  • 76
  • 77
  • 78
  • 79
  • 80
  • 81
  • 82
  • 83
  • 84
  • 85
  • 86
  • 87
  • 88
  • 89
  • 90
  • 91
  • 92
  • 93
  • 94
  • 95
  • 96
  • 97
  • 98
  • 99
  • 100
  • 101
  • 102
  • 103
  • 104
  • 105
  • 106
  • 107
  • 108
  • 109
  • 110
  • 111
  • 112
  • 113
  • 114
  • 115
  • 116
  • 117
  • 118
  • 119
  • 120
  • 121
  • 122
  • 123
  • 124
  • 125
  • 126
Routing Configuration
81
Example 2: Assigning Administrative Preferences to Static Routes
By default, static routes are assigned a preference value of 1. The following command changes this
default:
console#Config
ip route distance 20
exit
When you configure a static route, you can assign a preference value to it. The preference overrides the
setting inherited as the default value for static routes.
In this example, two static routes are defined to the same destination but with different next hops and
different preferences (25 and 30). The route with the higher preference will only be used when the
preferred route is unavailable:
console#Config
ip route 10.25.67.0 255.255.255.0 10.25.22.2 metric 25
ip route 10.25.67.0 255.255.255.0 10.25.21.0 metric 30
exit
Similarly, you can create two default routes—one preferred and the other used as a backup. In this
example, the preference values 1 and 10 are assigned:
console#Config
ip route default 10.25.67.2 1
ip route default 10.25.67.7 10
exit
Using Equal Cost Multipath
The equal cost multipath (ECMP) feature allows a router to use more than one next hop to forward
packets to a given destination prefix. It can be used to promote a more optimal use of network resources
and bandwidth.
A router that does not use ECMP forwards all packets to a given destination through a single next hop.
This next hop may be chosen from among several next hops that provide equally good routes to the
destination. For example, in Figure 4-7, Router A sends all traffic to destinations in Network D through
next hop NH1, even though the route through NH2 is equally good. Forwarding all traffic via NH1 may
cause Link A to be overloaded while Link B is not used at all.