Show Prefix Command

The show prefix command displays detailed information about a prefix or group of prefixes. It can give you useful insight into how the decision maker process makes its decisions.

When load optimization is enabled, the show prefix display will also contain labels adjacent to the prefix category indicating how the winner was chosen (see Chapter 2: WAN Cost and Load Optimization):

• r--winner was selected from the regular winner set
• e--winner was selected from the extended winner set
• h--all links hot; winner is “least hot”
• j--no eligible winner in the extended winner set at the threshold-table level appropriate for current usage; the decision-maker process had to jump to a higher level (indicates a narrow extended winner set; you should consider increasing the size)
• l--no eligible winners could be selected by the load optimization algorithm; winner selected by load balancing (current usage has exceeded the maximum total load configured at the highest level of your load threshold table; it means that either the table is not configured correctly or you have insufficient capacity to meet demand)

The level indicator label will be accompanied by the total load value configured for that level.

Links are labeled as follows:

• a--CNA has asserted the link to be the best path
• b--link selected by BGP
• h--link is categorized as hot by the CNA decision-maker process (see Determining the Winner Set in Chapter 2: WAN Cost and Load Optimization)
• i--data is invalid; link no longer considered reliable for this prefix
• o--outage detected; prefix is no longer generating measurement traffic
• r--link is in the regular winner set
• e--link is in the extended winner set
• w--link is the current winner link

More than one link may be identified as a BGP-selected link if you have multiple edge routers peered to your CNA system.

If two or more routers have equal-cost routes to the prefix, then the CNA system will label each link with a b (for BGP selection).

Routers which use a lower-cost path through one of the other edge routers in your system will not advertise these routes to the CNA system and therefore will not be assigned the b label.

The i and o link labels both indicate that a link is not receiving reliable data for the prefix, but they are very different conditions that trigger very different responses by the CNA system.

The i label signifies a problem between the CNA system and the edge router--the link is considered unreliable for the prefix. The link will no longer be considered adequately measured and will not be considered a candidate for route assertion until it has generated enough measurement traffic to once again pass the CNA system’s adequacy tests. (See the Winner Set discussion elsewhere in this chapter for conditions that must be met to be considered a candidate for assertion.)

The o label signifies a problem outside of your network that requires immediate attention on the part of the CNA system--a new performance route has been calculated and asserted so that your site can continue serving users in the affected prefix. See the Prefix Outage Control discussion elsewhere in this chapter for more information.

NOTE: Labels may occasionally appear to be incorrect for the data values displayed in the show prefix command output or snapshot report tables. The values are updated almost immediately as data is received, but the labels must be calculated by the CNA system’s internal decision maker process. There may be a small timing differential, resulting in a discrepancy between data and label. When this occurs, try entering the show prefix command again, or view a later snapshot report.