Ticket#20 – Default Route Not Propagating in BGP: Missing Network Statement Fixed [CCNP Enterprise]

Problem Summary

In a multi-site enterprise setup running eBGP, the edge router was configured with a static default route pointing to the internet. However, this default route was not being advertised to downstream routers via BGP.

Remote sites relied on the HQ BGP router to learn the default route. But when the static route was configured, the admin forgot to include it in the BGP advertisements. As a result, remote sites couldn’t reach the internet, even though the HQ router could.

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Symptoms Observed

• HQ router had internet access (static route to ISP worked)
• Remote branches had no default route in their routing table
• show ip bgp on branch showed no 0.0.0.0/0
• BGP session was up and healthy
• No filtering or route-maps applied
• Static route present, but not seen in BGP table on HQ

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Root Cause Analysis

The issue boiled down to BGP not advertising the default route, because:

• BGP only advertises networks explicitly mentioned using the network command
• The static route for 0.0.0.0/0 was present in the RIB (Routing Table) but not in the BGP table
• No network 0.0.0.0 statement = no BGP advertisement

Remember: BGP does NOT “automatically” advertise static or connected routes like IGPs do!

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The Fix

On the HQ router (BGP speaker), add the network statement with mask:

ip route 0.0.0.0 0.0.0.0 <next-hop-IP>
router bgp 65000
 network 0.0.0.0

This tells BGP:
“If you see this route in your routing table, advertise it to peers.”

Alternative (if using route-maps):

neighbor x.x.x.x default-originate

Use this only if you’re intending to force a default route to a peer, regardless of local availability.

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EVE-NG Lab Topology

• HQ has a static default route to ISP
• Branches have eBGP peering with HQ
• Default route not advertised from HQ until network 0.0.0.0 added

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Verification

Command	Purpose
show ip bgp	Check advertised prefixes
show ip route	Confirm default route in RIB
show ip bgp neighbors <ip> advertised-routes	Confirm default route is sent
debug ip bgp	Observe BGP updates live
`show run	section bgp`

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Key Takeaways

• BGP requires explicit network commands to advertise prefixes
• A static route alone is not enough
• Always verify both RIB and BGP table
• Use default-originate carefully—good for forced default push
• Lab it out before applying in production!

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Best Practices / Design Tips

• Use network 0.0.0.0 in HQ if default route exists in RIB
• Avoid unnecessary redistribution unless required
• Prefer route-maps with conditional default-originate for flexibility
• Monitor BGP advertisements with: bashCopyEditshow ip bgp neighbors x.x.x.x advertised-routes
• Automate verification via EEM or CLI scripts in critical environments

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FAQs

1. Why didn’t BGP advertise the default route automatically?
   Because BGP doesn’t auto-advertise any route—it needs a network command explicitly configured.
   
   
2. Does network 0.0.0.0 work without a static default route?
   No. The route must exist in the RIB, or BGP won’t advertise it.
   
   
3. How do I verify if BGP is advertising the default route?
   Use: show ip bgp neighbors <peer-IP> advertised-routes
   
   
4. Can I use redistribute static instead?
   Yes, but it’s not recommended unless you’re filtering properly—it can flood BGP with all static routes.
   
   
5. What is the difference between network and default-originate?
   • network: Advertises prefix if it exists in RIB
   • default-originate: Pushes 0.0.0.0/0 even if it doesn’t exist locally
     
     
6. Can I advertise default route via route-map?
   Yes, using neighbor x.x.x.x default-originate route-map <name> with conditions.
   
   
7. Is this behavior same in iBGP and eBGP?
   Yes. In both, default route must be manually advertised.
   
   
8. What’s the impact of not having a default route on branch routers?
   They won’t know where to send internet-bound traffic, causing “destination unreachable” errors.
   
   
9. Can I use aggregate-address 0.0.0.0 0.0.0.0?
   Technically yes, but it’s less common and requires special handling—network or default-originate is preferred.
   
   
10. What is the requirement for the network command to work?
    The prefix must exactly match a route in the routing table.
    
    
11. Why didn’t redistribute static work immediately?
    It might’ve worked, but without a proper route-map, you risk injecting all static routes, which is dangerous.
    
    
12. Should the default originate be used on all routers?
    No—only the router with external connectivity (typically edge/HQ).
    
    
13. What does the branch router see if default route is advertised?
    In the BGP table:

t*> 0.0.0.0/0 [20/0] via x.x.x.x

14. Can MPLS VPN customers receive default this way?
    Yes, using BGP default-originate under VRFs—common in MPLS L3VPN scenarios.
    
    
15. How to simulate this in EVE-NG?
    Build 3 routers (HQ, Branch, ISP), configure static default at HQ, BGP peering with branches, and observe default propagation.

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YouTube Video

Watch the Complete CCNP Enterprise: Default Route Not Propagating in BGP: Missing Network Statement Fixed Lab Demo & Explanation on our channel:

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Final Note

Understanding how to differentiate and implement Default Route Not Propagating in BGP: Missing Network Statement Fixed is critical for anyone pursuing CCNP Enterprise (ENCOR) certification or working in enterprise network roles. Use this guide in your practice labs, real-world projects, and interviews to show a solid grasp of architectural planning and CLI-level configuration skills.

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