I've read that sudo killall -HUP mDNSResponder;sudo killall mDNSResponderHelper;sudo dscacheutil -flushcache should flush the DNS cache on OSX (macOS Mojave). However, this command kills processes without restarting them, and is both hard to remember and cumbersome. Also, AFAIK dscacheutil applies only to the directory service. This is a staple Mac cleaning solution and this app is notarized by Apple. Flushing the DNS cache just so happens to be in its arsenal of features to help you do this. Mac apps like skitch. To flush the DNS cache with CleanMyMac all you’ll need to do is download it — you can do that here for free.
Apps for Network Tools. Network Analyzer Lite is a lite version of Network Analyzer - the ultimate tool for network analysis, LAN scanning and problem detection. Purchased Mac App after a couple of years of owning the iOS app. I have been using the iOS version for a couple of years now. I received the app for free on the app store as part of a weekly app lightlight promotion. I really like Clear on iOS and I today I purchsed the Mac version. I really like having access to my list on the Mac.
An interesting client problem in one of our multi-tenant data centers came to my attention the other day. A delay sensitive client noticed a slight increase in latency (20 ms) at very intermittent intervals from his servers in our data center to specific off-net destinations. The increase in latency was localized to the pair of Nexus 7000’s functioning as the core switch layer (CSW) and the layer3 edge for this particular data center. Beyond that all appeared normal on the N7K CSWs.
A TCP dump from a normal trunk interface attached to the N7Ks, showed unicast traffic on the N7K-2 device when the N7K-1 device was setup to receive internet traffic inbound and forward it into the data center client VLANs. Spotify premium free apk uptodown. The N7Ks are setup using the Cisco VPC (Virtual Port Channels).
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Upon investigating what appeared to be legitimate unicast traffic, the IP ARP tables showed the relevant destination MAC addresses, with the timers not indicating any recent problems. Mac how to show app bar. The host MAC addresses for these ARP entries however were absent in the CAM table. After forcing a refresh of both tables it was obvious that there was a problem with the MAC address entries, not refreshing as they should.
By this stage I had my suspicions about the problem but not yet the exact cause.
NX-OS has a range of very useful (yet poorly documented) internal system commands that offer a great deal more information than the usual show commands. Inspecting the L2FM (Layer2 Feature Manager) state for a given MAC address could verify my suspicions.
The command below showed a brief historical event log of the Layer 2 MAC Database.
The output above indicated why the MAC addresses were not seen in the CAM table. They were continually flushed.
This explained the rogue unicast traffic. What happens to unicast traffic with valid IP ARP entries, when no useable MAC addresses are available for forwarding? They are flooded using a mechanism known as unknown unicast flooding.
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With the problem described originally, the MAC flushes also explained the latency spikes, as one of the questionable VLAN’s belonged to a content provider, carrying large amounts of traffic. Every time the CDN hit a specific volume of traffic the unicast flooding increased the queue depths on certain N7Ks trunk links to customers. This, due to the large volumes of traffic, was enough to increase the latency for some customers.
Then to isolate the cause of the flushing MAC entries either the following system internal command:
When an MST switches receive TCN (Topology Change Notification), the associate MAC addresses in the CAM table are flushed. This is done to allow quicker convergence than the traditional STP implementation, but on the flip side, continual TCNs, have negative effect as seen here. In this case the TCNs were generated due to an incorrectly configured switch.
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– – – – For more information about how STP and MST operates be sure to go through the switching chapter in the Routing-Bits RS Handbook.