10 votes
Accepted

Why does EIGRP aim to be loop free?

All routing protocols try to avoid a loop topology. If there is a routing loop, data is not getting to the destination. If the path from source to destination is A -> B -> C -> D, but there is a ...
Ron Trunk's user avatar
  • 67.5k
6 votes
Accepted

How does STP convergence work?

I don't understand how a bridge decides that it is not connected to another bridge performing STP. If it doesn't hear BPDUs, then there's no bridge connected. How long will it until it decides ...
Ron Trunk's user avatar
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6 votes
Accepted

Cisco: err-disabled due to loop - but there are NO redundant physical paths/ wires/ connections

I think this might be related to a bug. This issue is documented in Cisco bug ID CSCea46385. To resolve the issue, you need to add the no keepalive command to the interface. Hope this helps you on ...
SleepyMan's user avatar
  • 2,016
6 votes
Accepted

What Happens If A Router Added To The Wrong Area Instead Of The Area 0?

1- Isn't OSPF a loop-free protocol? Shouldn't it avoid loops automatically? OSPF is loop-free precisely because all inter-area traffic must go through area 0 2- What happens if we add new router R8 ...
Ron Trunk's user avatar
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5 votes
Accepted

Connect a LAN cable to LAN1 & LAN2

You didn't actually connect two router ports, you connected two switch ports. The router has a switch module. You created a layer-2 broadcast storm. Broadcast is an essential part of ethernet. When a ...
Ron Maupin's user avatar
  • 99.6k
5 votes
Accepted

STP convergence process needs detailed explanation, please

It is a continuous process. It is continuous because the root bridge (or any other bridge) can fail. If root fails, new root needs to be selected, and if anyone else fails, affected part of the tree ...
Effie's user avatar
  • 1,828
4 votes

STP convergence process needs detailed explanation, please

The "election" is really a conceptual idea. Each bridge starts out sending its own bridge ID as the root bridge. If it hears a better ID, it starts sending that one. When all bridges are ...
Ron Trunk's user avatar
  • 67.5k
4 votes

How to create a routing loop?

If this was your setup: Host A ---- Router B ---- Router C ---- Router D ---- Host E Tell Router B that the network for Host E exists at Router C. Tell Router C that the network for Host E exists at ...
Eddie's user avatar
  • 15k
4 votes
Accepted

Connecting an SRX chassis cluster to redundant upstream WAN links

If I put two interfaces (one on each SRX) in a reth, is that sufficient to ensure that there won't be any loops? Yes* - reth interfaces are essentially a logical L3 interface - they will not loop ...
Benjamin Dale's user avatar
3 votes
Accepted

Is a networking loop considered a DoS attack?

If the network manager does something by mistake it's just pilot error; if I sneak into your building and do something to make trouble for you on purpose, it's an attack. If the attack is designed so ...
jonathanjo's user avatar
  • 16.2k
3 votes

Why does EIGRP aim to be loop free?

The TTL field in the IP header does not eliminate a routing loop. It just prevents the packets from being endlessly caught circling in the loop once it exists in that after 255 hops at most, they will ...
Peter Paluch's user avatar
3 votes
Accepted

Is STP used to prevent all traffic looping or just broadcast and multicast?

Actually, STP figures out the least-cost (shortest), loop-free path to the root switch. This is the path used for all traffic not directly attached to the switch. STP uses BPDUs to figure this out. ...
Ron Maupin's user avatar
  • 99.6k
3 votes

Routing the same prefix to different destinations on the same router

AIUI this is an application for vrfs. You have a "clean" vrf that faces the inside and a "dirty" vrf that reaches the outside. So effectively you would have two virtual routers one behind the other. ...
Peter Green's user avatar
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3 votes
Accepted

Prevent DHCP looping

Without knowing a lot more about your infrastructure... Disable the "data" port on all your phones. You appear to have dedicated voice and data ports to everyone, so there's no need for daisy ...
Ricky's user avatar
  • 32.2k
3 votes

Alternative Solution to Avoid Loop aside STP

There are three basic approaches here: Block the redundant link(s) using a spanning-tree protocol - MSTP, RSTP, STP or RPVST+. Aggregate the physical links into a single, logical link (link ...
Zac67's user avatar
  • 84.4k
3 votes

What Happens If A Router Added To The Wrong Area Instead Of The Area 0?

1- Isn't OSPF a loop-free protocol? Shouldn't it avoid loops automatically? Yes, and it will, if you follow it's design rules. Violating the rules might make it hard/impossible to detect a loop. At ...
Marc 'netztier' Luethi's user avatar
2 votes
Accepted

Is this topology loop free?

Switch uses Layer 2 Spanning Tree Protocol to ensures a loop free topology for any bridged Ethernet network. So if yours IOT device will forward bridge protocol data unit (BPDU) accross, switch will ...
Datagram.Network's user avatar
2 votes
Accepted

vpc loop avoidance scenario

The VPC peer link has a few special roles - it carries the CFSoE traffic (mentioned below) to allow the peers to sync (enabled automatically when feature vpc is turned on) and carries traffic for ...
rnxrx's user avatar
  • 6,114
2 votes

vpc loop avoidance scenario

I'm not quite sure CFS is the thing preventing loops. It is more about syncing and consistency checks. There's a simple rule though: do not send traffic out of member port if it was received over a ...
ar_'s user avatar
  • 1,133
2 votes

Prevent DHCP looping

Since you are considering changing switches, you can use mac-based-vlan on the switches (or voice-vlan). This will put the phones on a specific Vlan based on the MAC of your phones. Now all data ...
Golgot's user avatar
  • 427
2 votes
Accepted

Non [R]STP switches in LAN ring topology

If you plan to create a ring of switches, all those switches need to support RSTP or MSTP. That is, unless all the unmanaged switches completely ignore IEEE 802.1D and actually forward the RSTP BPDUs -...
Zac67's user avatar
  • 84.4k
2 votes

STP Loop issue on long distance link

xSTP is not a good choice when the link status (up/down) does not reflect actual L2 connectivity. Your diagram shows an L2 connection between BSN-1 and PHX-1 across different ISPs. Since that is very ...
Zac67's user avatar
  • 84.4k
2 votes

Spanning tree loop prevention

You should connect switches with trunk links and limit the VLANs allowed on each trunk to only those used on the switch with the switchport trunk allowed vlan <vlan list> command. Use the global ...
Ron Maupin's user avatar
  • 99.6k
2 votes

Spanning tree loop prevention

The most important thing is to select your root bridge by setting it to the lowest priority value. Default is 8/32768, the root should be 0/0 or 1/4096. The root bridge is the base of your spanning ...
Zac67's user avatar
  • 84.4k
2 votes

Loops in routers-same packet?

This is (one of the things) that the ID field in the IP packet is for. It should unique identify an IP packet for a particular source, destination, and protocol for the lifetime that a datagram is ...
richardb's user avatar
  • 1,598
2 votes
Accepted

Loops in routers-same packet?

There is nothing in the IPv4 header that enables you to identify duplicates. A packet is a duplicate when it matches a previous packet in entirety, header (apart from TTL and checksum) and payload, ...
Zac67's user avatar
  • 84.4k
1 vote

Why Poison Reverse is used in EIGRP routing protocol?

Poison reverse is used with split horizon. It helps prevent loops There is a Cisco document that explains it all (Hat tip to @ronmaupin)
Ron Trunk's user avatar
  • 67.5k
1 vote

Loop detection in Extreme switch

From the scarce information you're giving, a bridge loop seems to be created across that port. The most likely case would be that one of the wireless client has got a simultaneous, wired connection ...
Zac67's user avatar
  • 84.4k
1 vote
Accepted

How would a bridge loop occur?

A connected to B connected to C connected back to A. You now have a loop. A new frame arriving on an edge port on A will be sent to the links to B and C. They won't hand it back to A but they will ...
Ricky's user avatar
  • 32.2k
1 vote
Accepted

Cisco ASA looping broadcast packet

After upgrade to newer version 9.8.2 resolved all of the issue. Thanks for your support.
Satish's user avatar
  • 4,379

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