15 votes
Accepted

5 nines, how is it built from 4 nines links

4 nines = 99.99 %. That means the probability that a link fail is 0.01 % or 0.0001 in terms of probability (scale 0 - 1). Assuming independence, The probability that both link fails is 0.0001 x 0....
  • 18.5k
14 votes

5 nines, how is it built from 4 nines links

A link that is 99.99% reliable is down 0.01% or 0.0001 of the time. So if the downtime of the two links is independent then both lines will be simultaneously down 0.00000001 of the time. Your link is ...
  • 11.8k
9 votes

I have a single ethernet switch. Should I use spanning tree?

To add to Zac67's and JFL's answers: In case you decide to enable spanning-tree on the single switch, don't forget to configure the client's and server's switchports as Edge Ports (Cisco speak; ...
7 votes
Accepted

Dual ASA5510 with dual ISP failover

Assuming a single context active/passive failover configuration with the ASAs connecting to the 2911s on unique subnets, you could trunk the links using two subinterfaces and vlan tagging. But the ...
7 votes
Accepted

Two ISP bgp topology?

Even if you could still get PI IPv4 addresses in Asia: if your ISPs don't want to route your IP addresses then there is nothing you can do. Tunnels and LISP could solve some of your problems (I use ...
7 votes

Will STP lose data whilst switching from a failed link?

If i remember, default spanning tree (802.1d) takes about 50 secs to reconverge. That is the duration for which you will be losing frames. A link is detected down by the loss of 10 hello pkts. These ...
  • 585
6 votes
Accepted

Will STP lose data whilst switching from a failed link?

It is possible, even likely, that at least one (probably more) frames will be lost on any failover. The speed of the failover is highly dependent on what type of redundancy you are using. Spanning ...
  • 94.6k
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 ...
  • 63.6k
6 votes
Accepted

Network Redundancy with LACP Trunking

Scenario A: Switch 1 has ports 1+2 trunked together via LACP. They are plugged into Switch 2 ports 1+2. Both links will be used, but a single flow will only use one link. There is a hashing ...
  • 94.6k
6 votes

I have a single ethernet switch. Should I use spanning tree?

As explained by Zac67 answer STP is normally only useful when connecting several switches together. However there's other related features than can be useful on a standalone switch. BPDU Guard will ...
  • 18.5k
5 votes
Accepted

Network Ten LTE Hubs Into One Network

If you have access to 10 layer 3 switches you can certainly make this work. Treat each trailer as if it is a campus building with local internet. choose the trailer with the NAS as the core of the ...
5 votes
Accepted

Is it bad practice to use a Virtual Router for NTP-Clustering?

I can see a few ways of doing this: Round robin DNS with multiple A records (as suggested in comments by JFL). This would require the clients to properly re-look up the addresses when required, and ...
  • 15.9k
5 votes

PVST + MST + RSTP network. Possible to make it work?

Generally, you should stick to one spanning-tree protocol or only use those that interact well (e.g. MSTP and RSTP). Given the 1810 can only run RSTP that would be your choice. The downside of RSTP is ...
  • 72.9k
5 votes

I have a single ethernet switch. Should I use spanning tree?

STP protects your network in case two switch ports are connected together, so you should use it generally. With a single switch, you can have redundant links to an appropriately configured host. ...
  • 72.9k
4 votes
Accepted

Master stack switch turn off

This is true of Cisco Catalyst and as far as I know all Cisco switches: If you already have made both switches stack members, the slave switch should be elected to master if the current master ...
4 votes

Network redundancy design question with BGP

How should i perform failover link using BGP with same ISP? Form the BGP neighborship loopback interface. As per this thread: The use of a loopback interface ensures that the neighbor stays up ...
  • 2,317
4 votes

Reduce ARP cache time-out?

I have personally done that ARP timeout set to 60 sec for a single VLAN caused 0.05% ARP usage on cisco 29XX series. It is running like that for over a month. No problems at all. Still I'd not ...
4 votes
Accepted

Network redundancy with low cost switches in a ring

As long as your "expensive" switch runs Spanning Tree Protocol, you can connect your switches in a ring. STP will prevent packet storms by only allowing packets out one of its (ring) ports. But if ...
  • 63.6k
4 votes

Connect two routers to a single uplink for full redundancy

I have a single uplink with my ISP at a data center. I have 2 routers (CISCO 3850). How do I connect these routers to that uplink WITHOUT a network switch? That switch will be a single point of ...
  • 94.6k
4 votes

Network Ten LTE Hubs Into One Network

Two ideas... I think the typical way to handle it would be a router in every trailer with three subnets: one goes to a switch for a trailer LAN, one goes to a campus backbone LAN for access to ...
4 votes
Accepted

4507r Supervisor engines aren't operating redundantly

Redundancy on these Catalyst platforms operates in two modes: RPR (Route Processor Redundancy) and SSO (Stateful Switchover). In RPR mode, the Standby boots up "partially". When the Active dies for ...
  • 2,396
4 votes

Network Redundancy with LACP Trunking

From a functional point of view, there's no difference between LACP trunks and static trunks. All links are aggregated (with the limitations Ron has already pointed out) and the aggregation group is ...
  • 72.9k
3 votes
Accepted

Load balancing between multiple layer 3 switches

Actually if your access switches connected to the so called "core switches" have just one uplink, either to the HP or to the Juniper, full redundancy is not an option given your constraints of no ...
  • 266
3 votes
Accepted

Redundancy in Internet core and edge networks - redundant devices and redundant links

This would be entirely up to the Tier 1 and their strategy/business model and each one may handle this differently. Redundancy is about preventing loss of service first and preventing degradation of ...
  • 26.8k
3 votes

Connect one router to layer 3 3750-X stack for redundancy

You'll need another physical interface on your router that runs at the same speed as your existing physical interface. Once you have that, you can create an etherchannel/port-channel/lag between the ...
  • 1,783
3 votes
Accepted

Cisco HSRP with redundant links

I would use SVIs for the L3 interfaces at core instead of assigning the IP configuration to physical ports. This way, having VLAN 100 allowed in all links between Core1, Core2, Distribution1 and ...
3 votes
Accepted

Can I use an unmanaged switch as a substitute for redundant, stacked switches when using a single network card?

No. What you are proposing is to create a loop in your network with an unmanaged switch and then hoping it understands spanning-tree, or hoping that it forwards spanning-tree through itself so the ...
  • 1,470
3 votes
Accepted

Adding a switch to provide redundancy

Do you have enough router ports available to do this ? You would still have your five trunks between the two buildings, but an outage on SW1 wouldn't bring down the whole LAN anymore. You would need ...
3 votes
Accepted

BGP VPN created, how do I give access to internet

There are a few different ways to achieve what you are after. In my experience the easiest way to do this is to use vlans between the Service Provider "PE" router and the Customer "CE" router. One ...
3 votes

Fault tolerance with 3 routers in Packet Tracer

The simplest solution would be to add a dynamic routing protocol such as RIP, EIGRP or OSPF. Then raise the Administrative Distance of the static routes so the dynamically learned routes are ...
  • 1,241

Only top scored, non community-wiki answers of a minimum length are eligible