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Questions tagged [routing]

For questions about routing, the process of selecting to which network path traffic is sent. Consider using a more specific tag if your question is about a routing protocol like BGP or OSPF.

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Can the same network IPs be used more than once

Because of how routers separate networks is it possible to say use the network 192.168.1.0/24 several times as long as you have enough networks to separate? Example: 192.168.1.0/24 <--> 172.16.0....
Jason's user avatar
  • 1,015
2 votes
1 answer
375 views

Static routing in Linux [closed]

I want to know how static routes are evaluated in Linux. Have a few more specific questions. How are metrics used? If the packet is the last hop what do I put in the next hop field of the route? For ...
user673289's user avatar
13 votes
3 answers
12k views

OSPF Stuck in Exstart Adjacency State

According to this article two routers will get stuck in the exstart adjacency state when their configured MTU sizes do not match. Does a VLAN tag affect this as well even if the routers involved are ...
JDGray's user avatar
  • 311
3 votes
5 answers
26k views

Routing Serial cables instead of Ethernet

I am doing some CCNA training videos and using packet tracer and they showed using a serial cable to connect two routers. Why are serial cables used instead of Ethernet cables? Does it depend on the ...
Jason Pass's user avatar
3 votes
3 answers
663 views

How do apps know about asymmetric routing?

We made did a campus LAN upgrade recently, during which we migrated from a mixed EIGRP/OSPF IGP to a multi-area OSPF redistributing to/from BGP on our WAN. We have two entry points on different sides ...
Pseudocyber's user avatar
2 votes
2 answers
2k views

loopback ip issue

So I have a weird issue. If I configure a /30 ip on an ethernet interface, for example 10.10.10.1/30 on Router1 and 10.10.10.2/30 on an ethernet interface on Router2, I can ping each other fine...no ...
Network Samurai's user avatar
3 votes
1 answer
1k views

ASA Transparent Mode Route Lookup

In what situations will an ASA perform route lookup? (transparent mode)
hell yeah's user avatar
1 vote
3 answers
853 views

How to keep office LAN private from public WLAN [closed]

I handle the network at a small business; it's not my primary job but one that I am in charge of. My boss owns a house next to the office that he uses as a general meeting area and as a guest house ...
jwatts1980's user avatar
16 votes
2 answers
11k views

BGP multipath with different ASNs feasible for production networks?

on Cisco (this command is hidden for some reason) #bgp bestpath as-path multipath-relax The default BGP behavior only installs only routes with exact the same AS_PATH into RIB. With multipath-relax, ...
sdaffa23fdsf's user avatar
  • 1,281
6 votes
3 answers
318 views

/23 PI space - breakup

a client currently has a /23 PI space where the route-object is currently managed by ISP-A we want to split the PI space into two /24's but not certain on how best to go about this. ISP-A will use ...
DrBru's user avatar
  • 1,629
11 votes
3 answers
1k views

Do today's routers prevent fake IP headers?

I know people can modify the IP headers and change source IP address, but it should be simple for network devices to detect those messages. If they don't, why is it so hard? Does it add too much ...
Nachos's user avatar
  • 267
14 votes
6 answers
28k views

What happens when the ARP cache overflows?

In at least one implementation there is a hard limit on the capacity of the ARP table. What happens when the ARP cache is full and a packet is offered with a destination (or next-hop) that isn't ...
neirbowj's user avatar
  • 879
8 votes
1 answer
1k views

traffic engineering - policies for BGP vs static routes

Considering a transition of specific public Internet site via a new location. At the current location, I've got a static route configured in my Cisco router pointed to my internal firewall. The new ...
raidORlostark's user avatar
10 votes
3 answers
9k views

interpreting ping results

I'm pinging yahoo.com and am I'm puzzled by the result. C:\Users\jon>ping -t yahoo.com Pinging yahoo.com [98.138.253.109] with 32 bytes of data: Reply from 98.138.253.109: bytes=32 time=195ms TTL=...
jon's user avatar
  • 203
7 votes
2 answers
1k views

ISIS p2p on Ethernet media

I am looking for technical clarity on why someone should / shouldn’t use ISIS p2p topologies on Ethernet media. Ethernet is a broadcast medium , however if it’s configured as a p2p link with /31’s ...
DrBru's user avatar
  • 1,629
2 votes
1 answer
1k views

Portforwarding by Subdomain [closed]

I want to have multiple servers behind a single firewall and access each with a different subdomain. Currently, I am having to have each server tied to a different port (which my firewall forwards to ...
William's user avatar
  • 123
9 votes
2 answers
2k views

Can one configure several static EIGRP Neighbors on one interface?

Can one configure several static EIGRP Neighbors on one interface and are there any considerations apart from disabling split-horizon that one should consider?
Max's user avatar
  • 837
10 votes
5 answers
11k views

Asymetric routing - causes and effects?

It happens that I run across customers who have what I define as an "asymetric routing" in their networks. Simply said, they have two gateways on the same IP subnet. The clients are configured to ...
FlavioB's user avatar
  • 151
5 votes
4 answers
763 views

How risky is a personal-use-only wireless subnet inside the corporate subnet?

My company's security policy with respect to wireless routers is to not use them at all -- everyone's wired in. Devices for personal use, such as laptops or cell phones, have to use their phone's data ...
Logical Fallacy's user avatar
6 votes
1 answer
294 views

Why there is a maximum of 4096 queues in WFQ?

In QoS there is a variety of Queuing methods and one of them is WFQ, which organizes the flows in different queues where each queue has a weight that determines which flow will go first. Now for ...
Juan Jose Polanco Arias's user avatar
9 votes
2 answers
12k views

BGP remote-triggered blackhole (RTBH) filter for Juniper

I'm trying to find the most elegant way to implement a RTBH filter for routes received from a customer. The filter should: Only accept the customers own prefixes from a prefix-list Only accept /32 ...
Sebastian Wiesinger's user avatar
3 votes
1 answer
6k views

Routing table in QNX [closed]

I've an embedded system running on QNX 6.2.1. (I'll call it QNX box.) The QNX box has two network adaptors. I've configured the driver, so they appear as en0 and en1. Here are their IP settings: en0:...
Thanushan's user avatar
  • 143
7 votes
1 answer
1k views

Reliable connectivity to China [closed]

I have been struggling on getting reliable connectivity to China (AS4837 China Unicom Backbone, AS4134 China Telecom Backbone, AS4538 China Education and Research Network Center) On most links I have ...
sdaffa23fdsf's user avatar
  • 1,281
10 votes
3 answers
4k views

Inbound BGP load-balancing from same ISP router

I have two BGP routers for DIA with an issue with one provider in that the two links to this provider land on the same SP router. My ethernet handoffs via two separate MetroE links from another ...
generalnetworkerror's user avatar
4 votes
1 answer
4k views

Isolating Juniper Management Plane

Out of the box, it seems that the Juniper management routing is part of the default route table. Can I use logical systems to isolate the service plane from management routing? Are there any drawbacks?...
Dennis Olvany's user avatar
4 votes
2 answers
944 views

Setting the same gateway address at a DR site as our main site

I have a question about routed traffic across a site to site VPN between 2 Cisco ASA 5510's. We have our office side and our DR side and the question is could I have an IP conflict of gateway IP ...
Brett Polakowski's user avatar
11 votes
2 answers
2k views

RIP routing is broken between two routers

There are 2 routers connected something like this: Network1 ----- (172.16.1.1/24) Router 1 (172.16.3.1/30) ------ (172.16.3.2/30) Router 2 ------ (172.16.2.1/24) Network 2 I try to add addresses for ...
Random42's user avatar
  • 213
21 votes
3 answers
4k views

CEF operations on L3 switch vs router

I understand that L3 switches use CEF for faster packet forwarding. However, CEF will not work for packets that need to undergo NAT. Does this mean CEF isn't used by edge routers and edge L3 switches? ...
Michael May's user avatar
  • 1,005
11 votes
3 answers
869 views

Circular BGP propagation

This one is a difficult to describe, it's hypothetical because I'm learning about routing and right now I'm focused on BGP. Let's say my ASN is 65000, and I announce 192.0.2.0/24. My peer, AS 65001 ...
Libbux's user avatar
  • 515
10 votes
3 answers
12k views

Default-network and default-gateway

When would you choose to use the ip default-network command instead of the ip default-gateway command?
Adam Loveless's user avatar
10 votes
1 answer
8k views

What factors drive L2 vs L3 in the access layer?

When designing an access layer, best practices today seem to indicate going toward a L3 design. I know the answers may be different depending on whether or not we're talking about a DC design or ...
generalnetworkerror's user avatar
4 votes
2 answers
2k views

Is migrating to VRF or rolling-back an easy proposition?

If VRF is implemented for routing table separation such as having an overlay network for a guest network that doesn't mix with regular LAN routing, is migrating to it easily done on Cisco switches (...
generalnetworkerror's user avatar
6 votes
6 answers
2k views

What are the reasons for choosing separate or combined VPN and Internet routers?

Here's a network design question: I've just been reading "IPv6 for Enterprise Networks" by McFarland et. al. and it (among other Cisco documents) separates out Internet routing from remote access VPN. ...
Paul Gear's user avatar
  • 438
8 votes
3 answers
198 views

How to apply configuration after replacing Routing Engine(RE) for CISCO7609-S?

Senario: I have the backup configuration file. But I don't any USB drive or compact flash card. After replacing the Routing Engine, I tried to copy/paste the configs (around 12k lines) from the ...
Bo Cao's user avatar
  • 401
13 votes
1 answer
2k views

What is the difference between a VRF and GRF? (cisco)

I've heard about VRF's and GRF's, but was is the difference between those 2? (cisco)
Bulki's user avatar
  • 2,393
4 votes
7 answers
11k views

Dynamic Routing Protocol (IGP) over IPSec VPN tunnels to branch offices?

What are the best practices for running an IGP to learn networks at HQ from branch offices when those offices connect via IPSec LAN-to-LAN VPN tunnels over the Internet? The branch offices terminate ...
generalnetworkerror's user avatar
12 votes
6 answers
4k views

Best practice for dual-homing site with two ISPs?

I am subscribed to two ISPs, a fast expensive one and a cheap but slower one. They use different technologies, cable and ADSL, so there isn't much of a single point of failure, and all my comms ...
Morgaine's user avatar
  • 261
9 votes
1 answer
331 views

Remote Campus Routing Design

A third party provider supplies connectivity my remote satellite campus over metro ethernet. Due to red tape the provider is required to supply a routed point-to-point connection (R2 and R3) to the ...
Paul Garrett's user avatar
10 votes
3 answers
15k views

Cisco: prevent vlan's of communicating with eachother on cisco router (ACL alternative)

Setup: Cisco router with multiple VLAN's configured on it. How can you prevent 2 VLAN's communicating with eachother? Normally I would do this with ACL's like this: access-list 102 deny ip 1.1.1.0 0....
Bulki's user avatar
  • 2,393
7 votes
2 answers
4k views

VPN routing for hosts with multiple ip addresses [closed]

I use Mikrotik RouterOS as the NAT router. Some hosts behind the router also have a direct connection to the Internet and these hosts have a default route to the ISP's gateway instead of RouterOS. I ...
sdaffa23fdsf's user avatar
  • 1,281
16 votes
7 answers
111k views

What are the differences between VRRP and HSRP?

Are there any significant differences between VRRP and HSRP?
Bulki's user avatar
  • 2,393
23 votes
7 answers
41k views

Difference between access list and prefix list?

Can someone explain with an example whats the difference between an access list and prefix list.
NAVEEN GEORGE's user avatar
8 votes
3 answers
6k views

BGP - Soft Reset Outbound & Verification

My understanding of the command: clear ip bgp * soft out is that the router on which the command is issued will re-advertise everything it knows about BGP to it's neighbors. As I see it, it's as if ...
BrianK's user avatar
  • 325
40 votes
8 answers
34k views

How would a router with /32 WAN subnet mask communicate with the rest of the Internet?

I'm studying networking and one of the most basic things I've been told countless times is that computers can't communicate outside of their own subnet. On the other hand, by looking at some ADSL ...
AndrejaKo's user avatar
  • 695
11 votes
2 answers
4k views

Why don't iperf, scamper and path MTU discovery packet captures agree on the path's MTU?

Let's do some path MTU discovery between two Debian hosts separated by a Debian router that runs Shorewall-generated iptables rules. Each of the two hosts uses a single Ethernet link while the router ...
Jean-Marc Liotier's user avatar
8 votes
3 answers
27k views

Policy routing configuration in Fortigate

I have an scenario where a Fortigate firewall is used to separate internal networks from the Internet (FortiOS Version 4.0 MR3 patch 11). Right now there is a single Internet connection attached to ...
Daniel Yuste Aroca's user avatar
7 votes
4 answers
10k views

Distributing static routes across an OSPF area

If you have a router which does not support OSPF, but your routing topology makes use of OSPF as all other devices do support it, what is the best way to get this routers networks in to the OSPF area? ...
SimonJGreen's user avatar
  • 1,695
10 votes
3 answers
1k views

Routing with seperate WAN link for backups

We have two geographically separate data centers. We are preparing to implement a new WAN connection (dark cloud) that would be used only for backup traffic. The servers will have two NIC cards (...
Peter's user avatar
  • 1,361

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