network [network] mask [mask]
Advertises a specific network prefix into the BGP routing table for distribution to peers.
Definition: network [network] mask [mask] is a Cisco IOS router config command. Advertises a network into BGP. The specified network must exist in the local routing table (via static route, connected, or IGP) for BGP to originate and advertise it.
network <network-address> mask <subnet-mask>When to Use This Command
- Advertising a public IP block assigned by an ISP to BGP peers.
- Originating a summary route into BGP for load balancing or redundancy.
- Publishing enterprise subnets to the internet via eBGP.
- Injecting networks into BGP to be redistributed to other peers.
Command Examples
Advertise a /24 network to an ISP via eBGP
R1(config)# ip route 198.51.100.0 255.255.255.0 Null0
R1(config)# router bgp 65001
R1(config-router)# network 198.51.100.0 mask 255.255.255.0R1(config-router)#
A static route to Null0 ensures the exact prefix exists in the routing table. BGP then originates and advertises 198.51.100.0/24 to all configured peers.
Verify the network appears in the BGP table
R1# show ip bgp 198.51.100.0BGP routing table entry for 198.51.100.0/24, version 2
Paths: (1 available, best #1, table default)
Local
0.0.0.0 from 0.0.0.0 (10.0.0.1)
Origin IGP, metric 0, localpref 100, weight 32768, valid, sourced, local, bestThe '>' symbol (best) and 'Local' origin show this router originated the prefix. 'weight 32768' is the default for locally originated routes.
Understanding the Output
No direct output from the network command. Use 'show ip bgp' or 'show ip bgp [prefix]' to verify the network appears with a '>' (best) indicator. If the network is missing from the routing table (no static route, no connected, no IGP), BGP will NOT advertise it — this is a very common exam scenario.
CCNA Exam Tips
CCNA exam tip: BGP 'network' is NOT like OSPF/EIGRP 'network' — it does NOT enable BGP on interfaces. It advertises an exact prefix.
CCNA exam tip: The network must exist in the IP routing table EXACTLY as specified (exact match of network and mask). A /23 route won't satisfy a 'network x.x.x.x mask 255.255.255.0' statement.
CCNA exam tip: A common technique is 'ip route [prefix] [mask] Null0' to create a black-hole route so BGP can originate the summary.
CCNA exam tip: BGP will suppress the advertisement if the prefix disappears from the routing table.
Common Mistakes
Mistake 1: Omitting the 'mask' keyword — without it, BGP assumes a classful mask which may not match the intended prefix.
Mistake 2: Specifying a network that doesn't exist in the routing table — BGP silently ignores it.
Mistake 3: Confusing this with IGP network statements — BGP 'network' only advertises; it doesn't activate BGP on interfaces.
network [network] mask [mask] vs router bgp [asn]
The commands 'network [network] mask [mask]' and 'router bgp [asn]' are commonly confused because both are essential for BGP configuration but operate at different stages. 'router bgp [asn]' initiates the BGP process, while 'network [network] mask [mask]' advertises a specific network within that process.
| Aspect | network [network] mask [mask] | router bgp [asn] |
|---|---|---|
| Scope | Advertises a specific network prefix | Creates the entire BGP routing process |
| Configuration mode | Router configuration mode (under router bgp) | Global configuration mode |
| Dependency | Requires router bgp to be already configured | Prerequisite for any BGP subcommands |
| Effect | Adds network to BGP table for advertisement | Initiates BGP process and enters BGP config mode |
| Typical use order | After router bgp [asn] | First command in BGP configuration |
Use network [network] mask [mask] when you need to originate a specific prefix into BGP, ensuring it exists in the routing table.
Use router bgp [asn] when starting BGP configuration, to define the local AS number and enter BGP router configuration mode.
Related Commands
neighbor [ip] remote-as [asn]
Defines a BGP neighbor (peer) by specifying its IP address and AS number. If the remote AS matches the local AS, this creates an iBGP session; if different, it creates an eBGP session.
router bgp [asn]
Enters BGP router configuration mode and creates a BGP process with the specified autonomous system (AS) number. This is the first command required to configure BGP on a Cisco router.
show ip bgp
Displays the BGP routing table, showing learned BGP routes and their attributes, used for troubleshooting BGP path selection and verifying route advertisement.
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