In the day-to-day life of the Network and Internet area, it is very common for Internet Providers (ISPs) to have the need to carry out certain changes at controlled times, whenever there may be a considerable risk to the Network, due to some implementation, equipment migration , etc. And it is at this point that the so-called “maintenance windows” or “GMUD” fall into place.

The need to operate at a controlled time is due to the lower risk for the Network as a whole, as there is a general decrease in Network usage/traffic at dawn, just as on the other side there are also peak hours. “peak” periods such as lunch and evening periods, weekends and holidays (which in general can often see slightly higher traffic flow than midweek).

What is a “GMUD”?

When we talk about maintenance windows, there are some different terms about it but they refer to the same subject/purpose. If we use the term GMUD, it comes from “Change Management”, that is, changes to the ISP’s Network, in a strictly planned manner, which are normally carried out at controlled hours/dawn hours (examples: 4am, 5am, 6am…).

Given this, whenever it is necessary to schedule the execution of a GMUD / Window, it is extremely important to follow some “Check-Lists”, which help us not to leave “behind” any point necessary to be able to reach a window executed with quality and success!

To start with the more general explanations first, here are some observations that will always be helpful in preparing for a successful GMUD.

OBSs. general important:
  • Whenever possible, citing as an example a GMUD for physical replacement of a Router in the Network (replacement of an Asset), it is important to analyze the Network scenario in which you are working, and observe whether it is possible to plan an action plan to carry out a migration that does not leave everyone “blind”, that is, what would be the case when we remove all the cables from the Router in production, and plug them all into the New Router (and there is no redundancy, thus causing the loss of remote access to the ISP’s Network; hence the term “blindly”).
  • So, we recommend always validating with the ISP to carry out a migration in parts, in any way possible (but, of course, it will always depend on each case, scenario. There will be scenarios where this will not be possible);
  • Example: Taking the Consulting point of view (Made4it):
    • Still based on a Router migration (eg BGP; and that Router has more than 1 Link/Upstream), if at the time of migration it is possible to ‘turn’ only one cable to the New Router, referring to any of the Links that the customer has, so we migrated, and so (with an access also via some /30 with the old Router still in production) we managed to validate if that Link will ‘upload’ on the New Router;
    • Once ‘up’ and OK, we can perform external access to the new Router through the /30 IP on its side of such established Link;
    • And, therefore, we can migrate the rest of the Network much more calmly, since it was already approved the first time that the Link in the New Router established, and access to the equipment and the customer’s Network remained OK.
  • extra:
    • Note that, according to the analysis of the scenario, it may even be possible to carry out the activities/implementations/migrations in the ISP’s Network without even having the essential need for a Window/GMUD, if it is possible to carry out the changes in steps /phases, so that it does not affect the functioning of the Network.
    • And, whether with or without a window, always have a well-defined plan of action, so that there is no doubt about the real need, steps to be taken to achieve the desired objectives, etc.

However, regardless of the above factor, if it is indeed necessary to carry out a Window/GMUD, see below the CheckLists that are extremely important to be validated, always prior to the execution of a Window, so that everything can be well planned and , therefore, can obtain a satisfactory/expected result in the activities carried out.

Pre-GMUD ChecklistGeneral validations that an ISP needs to be aware of:

  • In case of Asset replacement, is the new equipment (Router, Switch, …) located in the same (physical) location as the current one that will be replaced? Is it in the same Rack, or different Racks? At the time of migration, will it be necessary to physically change some equipment from one Rack to another, or something similar? If so, has it been confirmed whether all the necessary tools are available to physically change the equipment in the Rack?
  • Will the current Asset/Equipment actually be 100% replaced or will it still remain on the Network fulfilling some function? (it will depend on each case, project, …)
  • Are the modules/GBICs and cords all available, as per the amount needed? Are there GBICs and spare cords? How many?
  • Are the modules/GBICs and cords from the same vendor, or different vendors? Have they all been tested? To make sure they are all working OK.
  • Is the Equipment (current/new) being (or will it be) powered by two power sources (to ensure redundancy)? And, if so, is each source connected to a different/separate UPS?
  • Is there a possibility that the ISP has a Console Cable (access tested before) to access the Router/Equipment directly if necessary? And even for GMUD executions in conjunction with the Consulting team (in this case, Made4it, for example), there is the possibility that, in extreme cases, the customer can route an internet connection from a mobile device to a notebook, so that he can provide us with an external access to this Console access? (a TeamViewer, AnyDesk, …, from the machine connected to the Router) (this would be to guarantee that you have access to the equipment referring to the changes, so that you can check if everything is in order, etc.)

Many times it may seem that we already have in mind everything necessary for a successful Window, but we always recommend validating this CheckList, since we are human and can forget points (even important ones), such as any of the details mentioned above, so to avoid this, and to have a successful conclusion of a Window/GMUD, carefully keep the information raised here, as it is certain that they will always be able to help in the preparation of a quality Window.

See below some more important points to be validated, a little more focused on the technical side (this would be what we, Made4it, would validate with ISPs before a GMUD).

Pre-GMUD checklistOther technical details:

  • Remove/always have a Backup of the Equipment/Assets involved in the maintenance, and attach it to the appropriate Documentation (both Made4it and the ISP);
    • (remembering that the Backup is important both BEFORE the Window and AFTER – with the new equipment implemented, for example…)
  • Prepare a SCHEDULED Maintenance Window notice email (sending to the Made team and the ISP team in question that is performing the demand that required the Window)
    • this is also important in the post-GMUD moment, having closed the Maintenance Window, an email with a description of everything that happened in the Window, to keep the Made team and the ISP aware;
    • : Regarding the warning email specifically, it is even recommended that it is always sent no later than lunchtime on the day before the Window, so that there is enough time for the entire team to be aware of the scheduled operation and planned.
  • Another very good issue is, for the migration, to have some draft / design of the Network to make the scenario involved clear (either a Topology design of the Physical Network, or Logical, or both (most recommended)).
  • And also, even for cases of equipment replacement (an improvement in Hardware, switching from such and such a BGP Vendor to such and such Vendor) a list (even if in plain text) of the interfaces of the old equipment that will be replaced can be very useful with new, for example:
  • MikroTik / / / / / / / NE40:
  • sfp+1 - - - - - - - -> GE0/3/3
  • sfp+5 - - - - - - - -> GE0/3/4
  • sfp+3 - - - - - - - -> GE0/3/5
  • sfp+4 - - - - - - - -> GE0/3/6
  • sfp+2 - - - - - - - -> GE0/3/7
  • sfp+6 - - - - - - - -> GE0/3/8
  • sfp+7 - - - - - - - -> GE0/3/9
  • sfp+8 - - - - - - - -> GE0/3/10

If you liked this content, be sure that by following these important recommendations mentioned above, the probability of having a successful maintenance window is even greater, once an action plan is prepared to be followed, pay attention to to the risks that may exist in the alterations, and we even do our best to protect ourselves from any unforeseen events, such as forgetting to validate an important point before performing the GMUD.

If you need technical support on your network, come and learn about our consulting service for internet providers, Made4ISP. To learn more, contact our commercial team.

Written by Bruno Martins. N3 Consultant, certified with Huawei HCIA R&S and JNCIA Junos